Ans: java.lang.reflect package has the ability to analyze itself in runtime. 28) What is interface ...... 2) class conditional { public static void main(String args[]) { int i = 20; int j = 55; int z = 0; ...... 1) String temp [] = new String {"j" "a" "z"};. 2) String ...
FREQUENTLY ASKED QUESTIONS (JAVA) IN INTERVIEWS
1)What is OOPs?
Ans: Object oriented programming organizes a program around its data,i.e.,objects and a set of well defined interfaces to that data.An object-oriented program can be characterized as data controlling access to code.
2)what is the difference between Procedural and OOPs? Ans: a) In procedural program, programming logic follows certain procedures and the instructions are executed one after another. In OOPs program, unit of program is object, which is nothing but combination of data and code. b) In procedural program,data is exposed to the whole program whereas in OOPs program,it is accessible with in the object and which in turn assures the security of the code.
3)What are Encapsulation, Inheritance and Polymorphism? Ans: Encapsulation is the mechanism that binds together code and data it manipulates and keeps both safe from outside interference and misuse. Inheritance is the process by which one object acquires the properties of another object. Polymorphism is the feature that allows one interface to be used for general class actions.
4)What is the difference between Assignment and Initialization? Ans: Assignment can be done as many times as desired whereas initialization can be done only once.
5)What are Class, Constructor and Primitive data types? Ans: Class is a template for multiple objects with similar features and it is a blue print for objects. It defines a type of object according to the data the object can hold and the operations the object can perform.
Constructor is a special kind of method that determines how an object is initialized when created.
Primitive data types are 8 types and they are: byte, short, int, long float, double boolean char
6)What is an Object and how do you allocate memory to it? Ans: Object is an instance of a class and it is a software unit that combines a structured set of data with a set of operations for inspecting and manipulating that data. When an object is created using new operator, memory is allocated to it.
7)What is the difference between constructor and method? Ans: Constructor will be automatically invoked when an object is created whereas method has to be called explicitly.
8)What are methods and how are they defined? Ans: Methods are functions that operate on instances of classes in which they are defined. Objects can
communicate with each other using methods and can call methods in other classes. Method definition has four parts. They are name of the method, type of object or primitive type the method returns, a list of parameters and the body of the method. A method's signature is a combination of the first three parts mentioned above.
9)What is the use of bin and lib in JDK? Ans: Bin contains all tools such as javac, appletviewer, awt tool, etc., whereas lib contains API and all packages.
10)What is casting? Ans: Casting is used to convert the value of one type to another.
11)How many ways can an argument be passed to a subroutine and explain them? Ans: An argument can be passed in two ways. They are passing by value and passing by reference. Passing by value: This method copies the value of an argument into the formal parameter of the subroutine. Passing by reference: In this method, a reference to an argument (not the value of the argument) is passed to the parameter.
12)What is the difference between an argument and a parameter? Ans: While defining method, variables passed in the method are called parameters. While using those methods, values passed to those variables are called arguments.
13)What are different types of access modifiers?
Ans: public: Any thing declared as public can be accessed from anywhere. private: Any thing declared as private can't be seen outside of its class. protected: Any thing declared as protected can be accessed by classes in the same package and subclasses in the other packages. default modifier : Can be accessed only to classes in the same package.
14)What is final, finalize() and finally? Ans: final : final keyword can be used for class, method and variables. A final class cannot be subclassed and it prevents other progr ammers from subclassing a secure class to invoke insecure methods. A final method can' t be overridden A final variable can't change from its initialized value.
finalize( ) : finalize( ) method is used just before an object is destroyed and can be called just prior to garbage collection. finally : finally, a key word used in exception handling, creates a block of code that will be executed after a try/catch block has completed and before the code following the try/catch block. The finally block will execute whether or not an exception is thrown. For example, if a method opens a file upon exit, then you will not want the code that closes the file to be bypassed by the exception-handling mechanism. This finally keyword is designed to address this contingency.
15)What is UNICODE? Ans: Unicode is used for internal representation of characters and strings and it uses 16 bits to represent each other.
16)What is Garbage Collection and how to call it explicitly? Ans: When an object is no longer referred to by any variable, java automatically reclaims memory used by that object. This is known as garbage collection. System.gc() method may be used to call it explicitly.
17)What is finalize() method ? Ans: finalize () method is used just before an object is destroyed and can be called just prior to garbage collection.
18)What are Transient and Volatile Modifiers? Ans: Transient: The transient modifier applies to variables only and it is not stored as part of its object's Persistent state. Transient variables are not serialized. Volatile: Volatile modifier applies to variables only and it tells the compiler that the variable modified by volatile can be changed unexpectedly by other parts of the program.
19)What is method overloading and method overriding? Ans: Method overloading: When a method in a class having the same method name with different arguments is said to be method overloading.
Method overriding : When a method in a class having the same method name with same arguments is said to be method overriding.
20)What is difference between overloading and overriding?
Ans: a) In overloading, there is a relationship between methods available in the same class whereas in overriding, there is relationship between a superclass method and subclass method. b) Overloading does not block inheritance from the superclass whereas overriding blocks inheritance from the superclass. c) In overloading, separate methods share the same name whereas in overriding,subclass method replaces the superclass. d) Overloading must have different method signatures whereas overriding must have same signature.
21) What is meant by Inheritance and what are its advantages? Ans: Inheritance is the process of inheriting all the features from a class. The advantages of inheritance are reusability of code and accessibility of variable s and methods of the super class by subclasses.
22)What is the difference between this() and super()? Ans: this() can be used to invoke a constructor of the same class whereas super() can be used to invoke a super class constructor.
23)What is the difference between superclass and subclass? Ans: A super class is a class that is inherited whereas sub class is a class that does the inheriting.
24) What modifiers may be used with top-level class? Ans: public, abstract and final can be used for top-level class.
25)What are inner class and anonymous class? Ans: Inner class : classes defined in other classes, including those defined in methods are called inner classes. An inner class can have any accessibility including private.
Anonymous class : Anonymous class is a class defined inside a method without a name and is instantiated and declared in the same place and cannot have explicit constructors.
26)What is a package? Ans: A package is a collection of classes and interfaces that provides a high-level layer of access protection and name space management.
27) What is a reflection package? Ans: java.lang.reflect package has the ability to analyze itself in runtime.
28) What is interface and its use? Ans:
Interface is similar to a class which may contain method's signature only but not bodies and it is a formal set of method and constant declarations that must be defined by the class that implements it.
Interfaces are useful for: a)Declaring methods that one or more classes are expected to implement b)Capturing similarities between unrelated classes without forcing a class relationship. c)Determining an object's programming interface without revealing the actual body of the class.
29) What is an abstract class? Ans: An abstract class is a class designed with implementation gaps for subclasses to fill in and is deliberately incomplete.
30) What is the difference between Integer and int? Ans: a) Integer is a class defined in the java.lang package, whereas int is a primitive data type defined in the Java language itself. Java does not automatically convert from one to the other. b) Integer can be used as an argument for a method that requires an object, whereas int can be used for calculations.
31) What is a cloneable interface and how many methods does it contain? Ans- It is not having any method because it is a TAGGED or MARKER interface.
32) What is the difference between abstract class and interface? Ans: a) All the methods declared inside an interface are abstract whereas abstract class must have at least one abstract method and others may be concrete or abstract.
b) In abstract class, key word abstract must be used for the methods whereas interface we need not use that keyword for the methods.
c) Abstract class must have subclasses whereas interface can't have subclasses.
33) Can you have an inner class inside a method and what variables can you access? Ans: Yes, we can have an inner class inside a method and final variables can be accessed.
34) What is the difference between String and String Buffer? Ans: a) String objects are constants and immutable whereas StringBuffer objects are not. b) String class supports constant strings whereas
StringBuffer class supports growable and modifiable strings.
35) What is the difference between Array and vector? Ans: Array is a set of related data type and static whereas vector is a growable array of objects and dynamic.
36) What is the difference between exception and error? Ans: The exception class defines mild error conditions that your program encounters. Ex: Arithmetic Exception, FilenotFound exception Exceptions can occur when -- try to open the file, which does not exist -- the network connection is disrupted -- operands being manipulated are out of prescribed ranges -- the class file you are interested in loading is missing The error class defines serious error conditions that you should not attempt to recover from. In most cases it is advisable to let the program terminate when such an error is encountered. Ex: Running out of memory error, Stack overflow error.
37) What is the difference between process and thread? Ans: Process is a program in execution whereas thread is a separate path of execution in a program.
38) What is multithreading and what are the methods for inter-thread communication and what is the class in which these methods are defined? Ans: Multithreading is the mechanism in which more than one thread run independent of each other within the process.
wait (), notify () and notifyAll() methods can be used for inter-thread communication and these methods are in Object class.
wait( ) : When a thread executes a call to wait( ) method, it surrenders the object lock and enters into a waiting state. notify( ) or notifyAll( ) : To remove a thre ad from the waiting state, some other thread must make a call to notify( ) or notifyAll( ) method on the same object.
39) What is the class and interface in java to create thread and which is the most advantageous method? Ans: Thread class and Runnable interface can be used to create threads and using Runnable interface is the most advantageous method to create threads because we need not extend thread class here.
40) What are the states associated in the thread? Ans: Thread contains ready, running, waiting and dead states.
41) What is synchronization? Ans: Synchronization is the mechanism that ensures that only one thread is accessed the resources at a time.
42) When you will synchronize a piece of your code? Ans: When you expect your code will be accessed by different threads and these threads may change a particular data causing data corruption.
43) What is deadlock? Ans: When two threads are waiting each other and can't precede the program is said to be deadlock.
44) What is daemon thread and which method is used to create the daemon thread?
Ans: Daemon thread is a low priority thread which runs intermittently in the back ground doing the garbage collection operation for the java runtime system. setDaemon method is used to create a daemon thread.
45) Are there any global variables in Java, which can be accessed by other part of your program? Ans: No, it is not the main method in which you define variables. Global variables is not possible because conce pt of encapsulation is eliminated here.
46)What is an applet? Ans: Applet is a dynamic and interactive program that runs inside a web page displayed by a java capable browser.
47)What is the difference between applications and applets? Ans: a)Application must be run on local machine whereas applet needs no explicit installation on local machine. b)Application must be run explicitly within a java-compatible virtual machine whereas applet loads and runs itself automatically in a java-enabled browser. d)Application starts execution with its main method whereas applet starts execution with its init method. e)Application can run with or without graphical user interface whereas applet must run within a graphical user interface.
48)How does applet recognize the height and width? Ans:Using getParameters() method.
49)When do you use codebase in applet? Ans:When the applet class file is not in the same directory, codebase is used.
50)What is the lifecycle of an applet?
Ans:init( ) method
- Can be called when an applet is first loaded
start( ) method
- Can be called each time an applet is started
paint( ) method
- Can be called when the applet is minimized or maximized
stop( ) method
- Can be used when the browser moves off the applet's page
destroy( ) method - Can be called when the browser is finished with the applet
51)How do you set security in applets? Ans: using setSecurityManager() method
52) What is an event and what are the models available for event handling? Ans: An event is an event object that describes a state of change in a source. In other words, event occurs when an action is generated, like pressing button, clicking mouse, selecting a list, etc. There are two types of models for handling events and they are: a) event-inheritance model and b) event-delegation model 53) What are the advantages of the model over the event-inheritance model? Ans: The event-delegation model has two advantages over the event-inheritance model. They are: a)It enables event handling by objects other than the ones that generate the events. This allows a clean separation between a component's design and its use. b)It performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to be repeatedly process unhandled events as is the case of the event inheritance.
54)What is source and listener ? Ans: source : A source is an object that generates an event. This occurs when the internal state of that object changes in some way.
listener : A listener is an object that is notified when an event occurs. It has two major requirements. First, it must have been registered with one or more sources to receive notifications about specific types of events. Second, it must implement methods to receive and process these notifications.
55) What is adapter class? Ans: An adapter class provides an empty implementation of all methods in an event listener interface. Adapter classes are useful when you want to receive and process only some of the events that are handled by a particular event listener interface. You can define a new class to act listener by extending one of the adapter classes and implementing only those events in which you are interested. For example, the MouseMotionAdapter class has two methods, mouseDragged( )and mouseMoved(). The signatures of these empty are exactly as defined in the MouseMotionListener interface. If you are interested in only mouse drag events, then you could simply extend MouseMotionAdapter and implement mouseDragged( ) .
56)What is meant by controls and what are different types of controls in AWT? Ans: Controls are components that allow a user to interact with your application and the AWT supports the following types of controls: Labels, Push Buttons, Check Boxes, Choice Lists, Lists, Scrollbars, Text Components. These controls are subclasses of Component.
57) What is the difference between choice and list? Ans: A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices and only one item may be selected from a choice. A List may be displayed in such a way that several list items are visible and it supports the selection of one or more list items.
58) What is the difference between scrollbar and scrollpane? Ans: A Scrollbar is a Component, but not a Container whereas Scrollpane is a Conatiner and handles its own events and perform its own scrolling.
59) What is a layout manager and what are different types of layout managers available in java.awt? Ans: A layout manager is an object that is used to organize components in a container. The different layouts are available are FlowLayout, BorderLayout, CardLayout, GridLayout and GridBagLayout.
60) How are the elements of different layouts organized? Ans: FlowLayout: The elements of a FlowLayout are organized in a top to bottom, left to right fashion. BorderLayout: The elements of a BorderLayout are organized at the borders (North, South, East and West) and the center of a container. CardLayout: The elements of a CardLayout are stacked, on top of the other, like a deck of cards. GridLayout: The elements of a GridLayout are of equal size and are laid out using the square of a grid.
GridBagLayout: The elements of a GridBagLayout are organized according to a grid. However, the elements are of different size and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes.
61) Which containers use a Border layout as their default layout? Ans: Window, Frame and Dialog classes use a BorderLayout as their layout.
62) Which containers use a Flow layout as their default layout? Ans: Panel and Applet classes use the FlowLayout as their default layout.
63) What are wrapper classes? Ans: Wrapper classes are classes that allow primitive types to be accessed as objects.
64) What are Vector, Hashtable, LinkedList and Enumeration? Ans: Vector : The Vector class provides the capability to implement a growable array of objects. Hashtable : The Hashtable class implements a Hashtable data structure. A Hashtable indexes and stores objects in a dictionary using hash codes as the object's keys. Hash codes are integer values that identify objects. LinkedList: Removing or inserting elements in the middle of an array can be done using LinkedList. A LinkedList stores each object in a separate link whereas an array stores object references in consecutive locations.
Enumeration: An object that implements the Enumeration interface generates a series of elements, one at a time. It has two methods, namely hasMoreElements( ) and nextElement( ). HasMoreElemnts( ) tests if this enumeration has more elements and nextElement method returns successive elements of the series.
65) What is the difference between set and list? Ans: Set stores elements in an unordered way but does not contain duplicate elements, whereas list stores elements in an ordered way but may contain duplicate elements.
66) What is a stream and what are the types of Streams and classes of the Streams? Ans: A Stream is an abstraction that either produces or consumes information. There are two types of Streams and they are: Byte Streams: Provide a convenient means for handling input and output of bytes. Character Streams: Provide a convenient means for handling input & output of characters. Byte Streams classes: Are defined by using two abstract classes, namely InputStream and OutputStream. Character Streams classes: Are defined by using two abstract classes, namely Reader and Writer.
67) What is the difference between Reader/Writer and InputStream/Output Stream? Ans: The Reader/Writer class is character-oriented and the InputStream/OutputStream class is byte -oriented.
68) What is an I/O filter?
Ans: An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another.
69) What is serialization and deserialization? Ans: Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects.
70) What is JDBC? Ans: JDBC is a set of Java API for executing SQL statements. This API consists of a set of classes and interfaces to enable programs to write pure Java Database applications.
71) What are drivers available? Ans: a)
JDBC-ODBC Bridge driver
b)
Native API Partly-Java driver
c)
JDBC-Net Pure Java driver
d)
Native-Protocol Pure Java driver
72) What is the difference between JDBC and ODBC? Ans: a)
OBDC is for Microsoft and JDBC is for Java applicati ons.
b)
ODBC can't be directly used with Java because it uses a C interface.
c)
ODBC makes use of pointers which have been removed totally from Java.
d) ODBC mixes simple and advanced features together and has complex options for simple queries. But JDBC is designed to keep things simple while allowing advanced capabilities when required.
e) ODBC requires manual installation of the ODBC driver manager and driver on all client machines. JDBC drivers are written in Java and JDBC code is automatically installable, secure, and portable on all platforms. f) JDBC API is a natural Java interface and is built on ODBC. JDBC retains some of the basic features of ODBC.
73) What are the types of JDBC Driver Models and explain them? Ans: There are two types of JDBC Driver Models and they are: a)
Two tier model and b) Three tier model
Two tier model: In this model, Java applications interact directly with the database. A JDBC driver is required to communicate with the particular database management system that is being accessed. SQL statements are sent to the database and the results are given to user. This model is referred to as client/server configuration where user is the client and the machine that has the database is called as the server. Three tier model: A middle tier is introduced in this model. The functions of this model are: a) Collection of SQL statements from the client and handing it over to the database, b)
Receiving results from database to the client and
c)
Maintaining control over accessing and updating of the above.
74) What are the steps involved for making a connection with a database or how do you connect to a database? Ans: a)
Loading the driver : To load the driver, Class.forName( ) method is used. Class.forName("sun.jdbc.odbc.JdbcOdbcDriver");
When the driver is loaded, it registers itself with the java.sql.DriverManager class as an available database driver. b)
Making a connection with database : To open a connection to a given database,
DriverManager.getConnection( ) method is used. Connection con = DriverManager.getConnection ("jdbc:odbc:somedb", "user", "password"); c) Executing SQL statements : To execute a SQL query, java.sql.statements class is used. createStatement( ) method of Connection to obtain a new Statement object. Statement stmt = con.createStatement( ); A query that returns data can be executed using the executeQuery( ) method of Statement. This method executes the statement and returns a java.sql.ResultSet that encapsulates the retrieved data: ResultSet rs = stmt.executeQuery("SELECT * FROM some table"); d) Process the results : ResultSet returns one row at a time. Next( ) method of ResultSet object can be called to move to the next row. The getString( ) and getObject( ) methods are used for retrieving column values: while(rs.next( ) ) { String event = rs.ge tString("event"); Object count = (Integer) rs.getObject("count"); 75) What type of driver did you use in project? Ans: JDBC-ODBC Bridge driver (is a driver that uses native(C language) libraries and makes calls to an existing ODBC driver to access a database engine).
76) What are the types of statements in JDBC? Ans: Statement SQL statement
-- To be used createStatement() method for executing single
PreparedStatement -- To be used preparedStatement() method for executing same SQL statement over and over
CallableStatement -- To be used prepareCall( ) method for multiple SQL statements over and over
77) What is stored procedure? Ans: Stored procedure is a group of SQL statements that forms a logical unit and performs a particular task. Stored Procedures are used to encapsulate a set of operations or queries to execute on database. Stored procedures can be compiled and executed with different parameters and results and may have any combination of input/output parameters.
78) How to create and call stored procedures? Ans: To create stored procedures: Create procedure procedurename (specify in, out and in out parameters) BEGIN Any multiple SQL statement; END;
To call stored procedures: CallableStatement csmt = con.prepareCall("{call procedure name(?,?)}"); csmt.registerOutParameter(column no., data type); csmt.setInt(column no., column name) csmt.execute( );
79) What is servlet?
Ans: Servlets are modules that extend request/response -oriented servers, such as java-enabled web servers. For example, a servlet might be responsible for taking data in an HTML order entry form and applying the business logic used to update a company's order database.
80) What are the classes and interfaces for servlets? Ans: There are two packages in servlets and they are javax.servlet and javax.servlet.http. Javax.servlet contains:
Interfaces
Classes
Servlet
Generic Servlet
ServletRequest
ServletInputStream
ServletResponse
ServletOutputStream
ServletConfig
ServletException
ServletContext
UnavailableException
SingleThreadModel
Javax.servlet.http contains:
Interfaces
Classes
HttpServletRequest
Cookie
HttpServletResponse
HttpServlet
HttpSession
HttpSessionBindingEvent
HttpSessionCintext
HttpUtils
HttpSeesionBindingListener
81) What is the difference between an applet and a servlet? Ans: a)
Servlets are to servers what applets are to browsers.
b) Applets must have graphical user interfaces whereas servlets have no graphical user interfaces.
82) What is the difference between doPost and doGet methods? Ans: a) doGet() method is used to get information, while doPost( ) method is used for posting information. b) doGet() requests can't send large amount of information and is limited to 240255 characters. However, doPost( )requests passes all of its data, of unlimited length. c) A doGet( ) request is appended to the request URL in a query string and this allows the exchange is visible to the client, whereas a doPost() request passes directly over the socket connection as part of its HTTP request body and the exchange are invisible to the client.
83) What is the life cycle of a servlet? Ans: Each Servlet has the same life cycle: a)
A server loads and initializes the servlet by init () method.
b)
The servlet handles zero or more client's requests through service( ) method.
c)
The server removes the servlet through destroy() method.
84) Who is loading the init() method of servlet? Ans: Web server
85) What are the different servers available for developing and deploying Servlets? Ans: a)
Java Web Server
b)
JRun
g)
Apache Server
h)
Netscape Information Server
i)
Web Logic
86) How many ways can we track client and what are they? Ans: The servlet API provides two ways to track client state and they are: a) Using Session tracking and b) Using Cookies.
87) What is session tracking and how do you track a user session in servlets? Ans: Session tracking is a mechanism that servlets use to maintain state about a series requests from the same user across some period of time. The methods used for session tracking are: a) User Authentication - occurs when a web server restricts access to some of its resources to only those clients that log in using a recognized username and password b) Hidden form fields - fields are added to an HTML form that are not displayed in the client's browser. When the form containing the fields is submitted, the fields are sent back to the server c) URL rewriting - every URL that the user clicks on is dynamically modified or rewritten to include extra information. The extra information can be in the form of extra path information, added parameters or some custom, server-specific URL change. d) Cookies - a bit of information that is sent by a web server to a browser and which can later be read back from that browser. e) HttpSession- places a limit on the number of sessions that can exist in memory. This limit is set in the session.maxresidents property
88) What is Server-Side Includes (SSI)?
Ans: Server-Side Includes allows embedding servlets within HTML pages using a special servlet tag. In many servlets that support servlets, a page can be processed by the server to include output from servlets at certain points inside the HTML page. This is accomplished using a special internal SSINCLUDE, which processes the servlet tags. SSINCLUDE servlet will be invoked whenever a file with an. shtml extension is requested. So HTML files that include server-side includes must be stored with an .shtml extension.
89) What are cookies and how will you use them? Ans: Cookies are a mechanism that a servlet uses to have a client hold a small amount of state-information associated with the user. a)
Create a cookie with the Cookie constructor: public Cookie(String name, String value)
b) A servlet can send a cookie to the client by passing a Cookie object to the addCookie() method of HttpServletResponse: public void HttpServletResponse.addCookie(Cookie cookie) c) A servlet retrieves cookies by calling the getCookies() method of HttpServletRequest: public Cookie[ ] HttpServletRequest.getCookie( ).
90) Is it possible to communicate from an applet to servlet and how many ways and how?
Ans: Yes, there are three ways to communicate from an applet to servlet and they are: a)
HTTP Communication(Text-based and object-based)
b)
Socket Communication
c)
RMI Communication
(You can say, by using URL object open the connection to server and get the InputStream from URLConnection object). Steps involved for applet-servlet communication: 1)
Get the server URL.
URL url = new URL(); 2)
Connect to the host
URLConnection Con = url.openConnection(); 3)
Initialize the connection
Con.setUseCatches(false): Con.setDoOutput(true); Con.setDoInput(true); 4) Data will be written to a byte array buffer so that we can tell the server the length of the data. ByteArrayOutputStream byteout = new ByteArrayOutputStream(); 5)
Create the OutputStream to be used to write the data to the buffer.
DataOutputStream out = new DataOutputStream(byteout);
91) What is connection pooling? Ans: With servlets, opening a database connection is a major bottleneck because we are creating and tearing down a new connection for every page request and the time taken to create connection will be more.
Creating a connection pool is an ideal approach for a complicated servlet. With a connection pool, we can duplicate only the resources we need to duplicate rather than the entire servlet. A connection pool can also intelligently manage the size of the pool and make sure each connection remains valid. A number of connection pool packages are currently available. Some like DbConnectionBroker are freely available from Java Exchange Works by creating an object that dispenses connections and connection Ids on request. The ConnectionPool class maintains a Hastable, using Connection objects as keys and Boolean values as stored values. The Boolean value indicates whether a connection is in use or not. A program calls getConnection( ) method of the ConnectionPool for getting Connection object it can use; it calls returnConnection( ) to give the connection back to the pool.
92) Why should we go for interservlet communication? Ans: Servlets running together in the same server communicate with each other in several ways. The three major reasons to use interservlet communication are: a) Direct servlet manipulation - allows to gain access to the other currently loaded servlets and perform certain tasks (through the ServletContext object) b)
Servlet reuse - allows the servlet to reuse the public methods of another servlet.
c) Servlet collaboration - requires to communicate with each other by sharing specific information (through method invocation)
93) Is it possible to call servlet with parameters in the URL? Ans: Yes. You can call a servlet with parameters in the syntax as (?Param1 = xxx || m2 = yyy).
94) What is Servlet chaining? Ans: Servlet chaining is a technique in which two or more servlets can cooperate in servicing a single request. In servlet chaining, one servlet's output is piped to the next servlet's input. This process continues until the last servlet is reached. Its output is then sent back to the client.
95) How do servlets handle multiple simultaneous requests? Ans: The server has multiple threads that are available to handle requests. When a request comes in, it is assigned to a thread, which calls a service method (for example: doGet(), doPost( ) and service( ) ) of the servlet. For this reason, a single servlet object can have its service methods called by many threads at once.
96) What is the difference between TCP/IP and UDP? Ans: TCP/IP is a two-way communication between the client and the server and it is a reliable and there is a confirmation regarding reaching the message to the destination. It is li ke a phone call. UDP is a one-way communication only between the client and the server and it is not a reliable and there is no confirmation regarding reaching the message to the destination. It is like a postal mail.
97) What is Inet address? Ans: Every computer connected to a network has an IP address. An IP address is a number that uniquely identifies each computer on the Net. An IP address is a 32-bit number.
98) What is Domain Naming Service(DNS)? Ans: It is very difficult to remember a set of numbers(IP address) to connect to the Internet. The Domain Naming Service(DNS) is used to overcome this problem. It maps one particular IP address to a string of characters. For example, www.mascom.com implies com is the domain name reserved for US commercial sites, moscom is the name of the company and www is the name of the specific computer, which is mascom's server.
99) What is URL? Ans: URL stands for Uniform Resource Locator and it points to resource files on the Internet. URL has four components: http://www.Pentafour.com:80/index.html http - protocol name, Pentafour - IP address or host name, 80 - port number and index.html - file path.
100) What is RMI and steps involved in developing an RMI object? Ans: Remote Method Invocation (RMI) allows java object that executes on one machine and to invoke the method of a Java object to execute on anothe r machine. The steps involved in developing an RMI object are: a)
Define the interfaces
b)
Implementing these interfaces
c)
Compile the interfaces and their implementations with the java compiler
d)
Compile the server implementation with RMI compiler
e)
Run the RMI registry
f)
Run the application
101) What is RMI architecture? Ans: - RMI architecture consists of four layers and each layer performs specific functions: a) Application layer
---- contains the actual object de finition
b) Proxy layer
---- consists of stub and skeleton
c) Remote Reference layer ---- gets the stream of bytes from the transport layer and sends it to the proxy layer d) Transportation layer to-machine communication
---- responsible for handling the actual machine-
102) what is UnicastRemoteObject? Ans: All remote objects must extend UnicastRemoteObject, which provides functionality that is needed to make objects available from remote machines.
103) Explain the methods, rebind( ) and lookup() in Naming class? Ans: rebind( ) of the Naming class(found in java.rmi) is used to update the RMI registry on the server machine. Naming. rebind("AddSever", AddServerImpl);
lookup( ) of the Naming class accepts one argument, the rmi URL and returns a reference to an object of type AddServerImpl.
104) What is a Java Bean? Ans: A Java Bean is a software component that has been designed to be reusable in a variety of different environments.
105) What is a Jar file? Ans: Jar file allows to efficiently deploying a set of classes and their associated resources. The elements in a jar file are compressed, which makes downloading a Jar file much faster than separately downloading several uncompressed files. The package java.util.zip contains classes that read and write jar files.
106) What is BDK? Ans: BDK, Bean Development Kit is a tool that enables to create, configure and connect a set of set of Beans and it can be used to test Beans without writing a code.
107) What is JSP? Ans: JSP is a dynamic scripting capability for web pages that allows Java as well as a few special tags to be embedded into a web file (HTML/XML, etc). The suffix traditionally ends with .jsp to indicate to the web server that the file is a JSP files. JSP is a server side technology - you can't do any client side validation with it. The advantages are: a) The JSP assists in making the HTML more functional. Servlets on the other hand allow outputting of HTML but it is a tedious process.
b) It is easy to make a change and then let the JSP capability of the web server you are using deal with compiling it into a servlet and running it.
108) What are JSP scripting elements? Ans: JSP scripting elements lets to insert Java code into the servlet that will be generated from the current JSP page. There are three forms: a) Expressions of the form that are evaluated and inserted into the output, b) Scriptlets of the form that are inserted into the servlet's service method, and c) Declarations of the form that are inserted into the body of the servlet class, outside of any existing methods.
109) What are JSP Directives? Ans: A JSP directive affects the overall structure of the servlet class. It usually has the following form: However, you can also combine multiple attribute settings for a single directive, as follows: There are two main types of directive: page, which lets to do things like import classes, customize the servlet superclass, and the like; and include, which lets to insert a file into the servlet class at the time the JSP file is translated into a servlet
110) What are Predefined variables or implicit objects?
Ans: To simplify code in JSP expressions and scriptlets, we can use eight automatically defined variables, sometimes called implicit objects. They are request, response, out, session, application, config, pageContext, and page.
111) What are JSP ACTIONS? Ans: JSP actions use constructs in XML syntax to control the behavior of the servlet engine. You can dynamically insert a file, reuse JavaBeans components, forward the user to another page, or generate HTML for the Java plugin. Available actions include: ?
jsp:include - Include a file at the time the page is requested.
?
jsp:useBean - Find or instantiate a JavaBean.
?
jsp:setProperty - Set the property of a JavaBean.
?
jsp:getProperty - Insert the property of a JavaBean into the output.
?
jsp:forward - Forward the requester to a newpage.
?
Jsp: plugin - Generate browser-specific code that makes an OBJECT or EMBED
112) How do you pass data (including JavaBeans) to a JSP from a servlet? Ans: (1) Request Lifetime: Using this technique to pass beans, a request dispatcher (using either "include" or forward") can be called. This bean will disappear after processing this request has been completed. Servlet: request.setAttribute("theBean", myBean); RequestDispatcher rd = getServletContext().getRequestDispatcher("thepage.jsp"); rd.forward(request, response); JSP PAGE:
(2) Session Lifetime: Using this technique to pass beans that are relevant to a particular session (such as in individual user login) over a number of requests. This bean will disappear when the session is invalidated or it times out, or when you remove it. Servlet: HttpSession session = request.getSession(true); session.putValue("theBean", myBean); /* You can do a request dispatcher here, or just let the bean be visible on the next request */ JSP Page: 3) Application Lifetime: Using this technique to pass beans that are re levant to all servlets and JSP pages in a particular app, for all users. For example, I use this to make a JDBC connection pool object available to the various servlets and JSP pages in my apps. This bean will disappear when the servlet engine is shut down, or when you remove it. Servlet: GetServletContext(). setAttribute("theBean", myBean); JSP PAGE:
113) How can I set a cookie in JSP? Ans: response.setHeader("Set-Cookie", "cookie string"); To give the response -object to a bean, write a method setResponse (HttpServletResponse response) - to the bean, and in jsp-file:
114) How can I delete a cookie with JSP? Ans: Say that I have a cookie called "foo," that I set a while ago & I want it to go away. I simply:
115) How are Servlets and JSP Pages related? Ans: JSP pages are focused around HTML (or XML) with Java codes and JSP tags inside them. When a web server that has JSP support is asked for a JSP page, it checks to see if it has already compiled the page into a servlet. Thus, JSP pages become servlets and are transformed into pure Java and then compiled, loaded into the server and executed.
1.The Java interpreter is used for the execution of the source code. True False Ans: a. 2) On successful compilation a file with the class extension is created. a) True b) False Ans: a. 3) The Java source code can be created in a Notepad editor. a) True b) False Ans: a. 4) The Java Program is enclosed in a class definition. a) True b) False Ans: a. 5) What declarations are required for every Java application? Ans: A class and the main( ) method declarations. 6) What are the two parts in executing a Java program and their purposes? Ans: Two parts in exe cuting a Java program are: Java Compiler and Java Interpreter. The Java Compiler is used for compilation and the Java Interpreter is used for execution of the application. 7) What are the three OOPs principles and define them? Ans : Encapsulation, Inheritance and Polymorphism are the three OOPs Principles.
Encapsulation: Is the Mechanism that binds together code and the data it manipulates, and keeps both safe from outside interference and misuse. Inheritance: Is the process by which one object acquires the properties of another object. Polymorphism: Is a feature that allows one interface to be used for a general class of actions.
8) What is a compilation unit? Ans : Java source code file. 9) What output is displayed as the result of executing the following statement? System.out.println("// Looks like a comment."); // Looks like a comment The statement results in a compilation error Looks like a comment No output is displayed Ans : a. 10) In order for a source code file, containing the public class Test, to successfully compile, which of the following must be true? It must have a package statement It must be named Test.java It must import java.lang It must declare a public class named Test Ans : b 11) What are identifiers and what is naming convention? Ans : Identifiers are used for class names, method names and variable names. An identifier may be any descriptive sequence of upper case & lower case letters,numbers or underscore or dollar sign and must not begin with numbers.
12) What is the return type of program’s main( ) method? Ans : void 13) What is the argument type of program’s main( ) method? Ans : string array. 14) Which characters are as first characters of an identifier? Ans : A – Z, a – z, _ ,$ 15) What are different comments? Ans : 1) // -- single line comment 2) /* -*/ multiple line comment 3) /** -*/ documentation 16) What is the difference between constructor method and method? Ans : Constructor will be automatically invoked when an object is created. Whereas method has to be call explicitly. 17) What is the use of bin and lib in JDK? Ans : Bin contains all tools such as javac, applet viewer, awt tool etc., whereas Lib contains all packages and variables.
Data types,variables and Arrays 1) What is meant by variable? Ans: Variables are locations in memory that can hold values. Before assigning any value to a variable, it must be declared. 2) What are the kinds of variables in Java? What are their uses? Ans: Java has three kinds of variables namely, the instance variable, the local variable and the class variable. Local variables are used inside blocks as counters or in methods as temporary variables and are used to store information needed by a single method.
Instance variables are used to define attributes or the state of a particular object and are used to store information needed by multiple methods in the objects. Class variables are global to a class and to all the instances of the class and are useful for communicating between different objects of all the same class or keeping track of global states. 3) How are the variables declared? Ans: Variables can be declared anywhere in the method definition and can be initialized during their declaration.They are commonly declared before usage at the beginning of the definition. Variables with the same data type can be declared together. Local variables must be given a value before usage. 4) What are variable types? Ans: Variable types can be any data type that java supports, which includes the eight primitive data types, the name of a class or interface and an array. 5) How do you assign values to variables? Ans: Values are assigned to variables using the assignment operator =. 6) What is a literal? How many types of literals are there? Ans: A literal represents a value of a certain type where the type describes how that value behaves. There are different types of literals namely number literals, character literals, boolean literals, string literals,etc. 7) What is an array? Ans: An array is an object that stores a list of items. 8) How do you declare an array? Ans: Array variable indicates the type of object that the array holds. Ex: int arr[]; 9) Java supports multidimensional arrays. a)True b)False
Ans: a. 10) An array of arrays can be created. a)True b)False Ans: a. 11) What is a string? Ans: A combination of characters is called as string. 12) Strings are instances of the class String. a)True b)False Ans: a. 13) When a string literal is used in the program, Java automatically creates instances of the string class. a)True b)False Ans: a. 14) Which operator is to create and concatenate string? Ans: Addition operator(+). 15) Which of the following declare an array of string objects? String[ ] s; String [ ]s: String[ s]: String s[ ]: Ans : a, b and d 16) What is the value of a[3] as the result of the following array declaration? 1
2 3 4 Ans : d 17) Which of the following are primitive types? byte String integer Float Ans : a. 18) What is the range of the char type? 0 to 216 0 to 215 0 to 216-1 0 to 215-1 Ans. d 19) What are primitive data types? Ans : byte, short, int, long float, double boolean char 20) What are default values of different primitive types? Ans : int - 0 short - 0 byte - 0 long - 0 l
float - 0.0 f double - 0.0 d boolean - false char - null 21) Converting of primitive types to objects can be explicitly. a)True b)False Ans: b. 22) How do we change the values of the elements of the array? Ans : The array subscript expression can be used to change the values of the elements of the array. 23) What is final varaible? Ans : If a variable is declared as final variable, then you can not change its value. It becomes constant. 24) What is static variable? Ans : Static variables are shared by all instances of a class.
Operators 1) What are operators and what are the various types of operators available in Java? Ans: Operators are special symbols used in expressions. The following are the types of operators: Arithmetic operators, Assignment operators, Increment & Decrement operators, Logical operators, Biwise operators, Comparison/Relational operators and
Conditional operators 2) The ++ operator is used for incrementing and the -- operator is used for decrementing. a)True b)False Ans: a. 3) Comparison/Logical operators are used for testing and magnitude. a)True b)False Ans: a. 4) Character literals are stored as unicode characters. a)True b)False Ans: a. 5) What are the Logical operators? Ans: OR(|), AND(&), XOR(^) AND NOT(~). 6) What is the % operator? Ans : % operator is the modulo operator or reminder operator. It returns the reminder of dividing the first operand by second operand. 7) What is the value of 111 % 13? 3 5 7 9 Ans : c. 8) Is &&= a valid operator?
Ans : No. 9) Can a double value be cast to a byte? Ans : Yes 10) Can a byte object be cast to a double value ? Ans : No. An object cannot be cast to a primitive value. 11) What are order of precedence and associativity? Ans : Order of precedence the order in which operators are evaluated in expressions. Associativity determines whether an expression is evaluated left-right or right-left. 12) Which Java operator is right associativity? Ans : = operator. 13) What is the difference between prefix and postfix of -- and ++ operators? Ans : The prefix form returns the increment or decrement operation and returns the value of the increment or decrement operation. The postfix form returns the current value of all of the expression and then performs the increment or decrement operation on that value. 14) What is the result of expression 5.45 + "3,2"? The double value 8.6 The string ""8.6" The long value 8. The String "5.453.2" Ans : d 15) What are the values of x and y ? x = 5; y = ++x; Ans : x = 6; y = 6 16) What are the values of x and z? x = 5; z = x++;
Ans : x = 6; z = 5
Control Statements 1) What are the programming constructs? Ans: a) Sequential b) Selection -- if and switch statements c) Iteration -- for loop, while loop and do-while loop 2) class conditional { public static void main(String args[]) { int i = 20; int j = 55; int z = 0; z = i < j ? i : j; // ternary operator System.out.println("The value assigned is " + z); } } What is output of the above program? Ans: The value assigned is 20 3) The switch statement does not require a break. a)True b)False Ans: b. 4) The conditional operator is otherwise known as the ternary operator. a)True b)False Ans: a.
5) The while loop repeats a set of code while the condition is false. a)True b)False Ans: b. 6) The do-while loop repeats a set of code atleast once before the condition is tested. a)True b)False Ans: a. 7) What are difference between break and continue? Ans: The break keyword halts the execution of the current loop and forces control out of the loop. The continue is similar to break, except that instead of halting the execution of the loop, it starts the next iteration. 8) The for loop repeats a set of statements a certain number of times until a condition is matched. a)True b)False Ans: a. 9) Can a for statement loop indefintely? Ans : Yes. 10) What is the difference between while statement and a do statement/ Ans : A while statement checks at the beginning of a loop to see whether the next loop iteration should occur. A do statement checks at the end of a loop to see whether the next iteration of a loop should occur. The do statement will always execute the body of a loop at least once. Introduction to Classes and Methods 1) Which is used to get the value of the instance variables? Ans: Dot notation.
2) The new operator creates a single instance named class and returns a reference to that object. a)True b)False Ans: a. 3) A class is a template for multiple objects with similar features. a)True b)False Ans: a. 4) What is mean by garbage collection? Ans: When an object is no longer referred to by any variable, Java automatically reclaims memory used by that object. This is known as garbage collection.
5) What are methods and how are they defined? Ans: Methods are functions that operate on instances of classes in which they are defined.Objects can communicate with each other using methods and can call methods in other classes. Method definition has four parts. They are name of the method, type of object or primitive type the method returns, a list of parameters and the body of the method. A method's signature is a combination of the first three parts mentioned above.
6) What is calling method? Ans: Calling methods are similar to calling or referring to an instance variable. These methods are accessed using dot notation. Ex: obj.methodname(param1,param2)
7) Which method is used to determine the class of an object?
Ans: getClass( ) method can be used to find out what class the belongs to. This class is defined in the object class and is available to all objects.
8) All the classes in java.lang package are automatically imported when a program is compiled. a)True b)False Ans: a.
9) How can class be imported to a program? Ans: To import a class, the import keyword should be used as shown.; import classname;
10) How can class be imported from a package to a program? Ans: import java . packagename . classname (or) import java.package name.*;
11) What is a constructor? Ans: A constructor is a special kind of method that determines how an object is initialized when created.
12) Which keyword is used to create an instance of a class? Ans: new.
13) Which method is used to garbage collect an object? Ans: finalize ().
14) Constructors can be overloaded like regular methods. a)True b)False Ans: a.
15) What is casting? Ans: Casting is bused to convert the value of one type to another.
16) Casting between primitive types allows conversion of one primitive type to another. a)True b)False Ans: a.
17) Casting occurs commonly between numeric types. a)True b)False Ans: a.
18) Boolean values can be cast into any other primitive type. a)True b)False Ans: b.
19) Casting does not affect the original object or value. a)True b)False
Ans: a.
20) Which cast must be used to convert a larger value into a smaller one? Ans: Explicit cast.
21) Which cast must be used to cast an object to another class? Ans: Specific cast.
22) Which of the following features are common to both Java & C++? A.The class declaration b.The access modifiers c.The encapsulation of data & methods with in objects d.The use of pointers Ans: a,b,c. 23) Which of the following statements accurately describe the use of access modifiers within a class definition? a.They can be applied to both data & methods b.They must precede a class's data variables or methods c.They can follow a class's data variables or methods d.They can appear in any order e.They must be applied to data variables first and then to methods Ans: a,b,d.
24) Suppose a given instance variable has been declared private. Can this instance variable be manipulated by methods out side its class? a.yes
b.no Ans: b.
25) Which of the following statements can be used to describe a public method? a.It is accessible to all other classes in the hierarchy b.It is accessablde only to subclasses of its parent class c.It represents the public interface of its class d.The only way to gain access to this method is by calling one of the public class methods Ans: a,c.
26) Which of the following types of class members can be part of the internal part of a class? a.Public instance variables b.Private instance variables c.Public methods d.Private methods Ans: b,d. 27) You would use the ____ operator to create a single instance of a named class. a.new b.dot Ans: a. 28) Which of the following statements correctly describes the relation between an object and the instance variable it stores? a.Each new object has its own distinctive set of instance variables b.Each object has a copy of the instance variables of its class c.the instance variable of each object are seperate from the variables of other objects
d.The instance variables of each object are stored together with the variables of other objects Ans: a,b,c. 29) If no input parameters are specified in a method declaration then the declaration will include __. a.an empty set of parantheses b.the term void Ans: a. 30) What are the functions of the dot(.) operator? a.It enables you to access instance variables of any objects wi thin a class b.It enables you to store values in instance variables of an object c.It is used to call object methods d.It is to create a new object Ans: a,b,c. 31) Which of the following can be referenced by this variable? a.The instance variables of a class only b.The methods of a class only c.The instance variables and methods of a class Ans: c. 32) The this reference is used in conjunction with ___methods. a.static b.non-static Ans: b. 33) Which of the following operators are used in conjunction with the this and super references? a.The new operator b.The instanceof operator
c.The dot operator Ans: c. 34) A constructor is automatically called when an object is instantiated a. true b. false Ans: a. 35) When may a constructor be called without specifying arguments? a. When the default constructor is not called b. When the name of the constructor differs from that of the class c. When there are no constructors for the class Ans: c. 36) Each class in java can have a finalizer method a. true b.false Ans: a. 37) When an object is referenced, does this mean that it has been identified by the finalizer method for garbage collection? a.yes b.no Ans: b. 38) Because finalize () belongs to the java.lang.Object class, it is present in all ___. a.objects b.classes c.methods Ans: b. 39) Identify the true statements about finalization.
a.A class may have only one finalize method b.Finalizers are mostly used with simple classes c.Finalizer overloading is not allowed Ans: a,c. 40) When you write finalize() method for your class, you are overriding a finalizer inherited from a super class. a.true b.false Ans: a. 41) Java memory management mechanism garbage collects objects which are no longer referenced a true b.false Ans: a. 42) are objects referenced by a variable candidates for garbage collection when the variable goes out of scope? a yes b. no Ans: a. 43) Java's garbage collector runs as a ___ priority thread waiting for __priority threads to relinquish the processor. a.high b.low Ans: a,b.
44) The garbage collector will run immediately when the system is out of memory a.true
b.false Ans: a.
45) You can explicitly drop a object reference by setting the value of a variable whose data type is a reference type to ___ Ans: null
46) When might your program wish to run the garbage collecter? a. before it enters a compute -intense section of code b. before it enters a memory-intense section of code c. before objects are finalized d. when it knows there will be some idle time Ans: a,b,d
47) For externalizable objects the class is solely responsible for the external format of its contents a.true b.false Ans: a
48) When an object is stored, are all of the objects that are reachable from that object stored as well? a.true b.false Ans: a
49) The default__ of objects protects private and trancient data, and supports the __ of the classes
a.evolution b.encoding Ans: b,a.
50) Which are keywords in Java? a) NULL b) sizeof c) friend d) extends e) synchronized Ans : d and e
51) When must the main class and the file name coincide? Ans :When class is declared public. 52) What are different modifiers? Ans : public, private, protected, default, static, trancient, volatile, final, abstract. 53) What are access modifiers? Ans : public, private, protected, default. 54) What is meant by "Passing by value" and " Passing by reference"? Ans : objects – pass by referrence Methods - pass by value 55) Is a class a subclass of itself? Ans : A class is a subclass itself.
56) What modifiers may be used with top-level class? Ans : public, abstract, final.
57) What is an example of polymorphism? Inner class Anonymous classes Method overloading Method overriding Ans : c
Packages and interface 1) What are packages ? what is use of packages ? Ans :The package statement defines a name space in which classes are stored.If you omit the package, the classes are put into the default package. Signature... package pkg; Use: * It specifies to which package the classes defined in a file belongs to. * Pa ckage is both naming and a visibility control mechanism. 2) What is difference between importing "java.applet.Applet" and "java.applet.*;" ? Ans :"java.applet.Applet" will import only the class Applet from the package java.applet Where as "java.applet.*" will import all the classes from java.applet package. 3) What do you understand by package access specifier? Ans : public: Anything declared as public can be accessed from anywhere private: Anything declared in the private can’t be seen outside of its clas s. default: It is visible to subclasses as well as to other classes in the same package. 4) What is interface? What is use of interface? Ans : It is similar to class which may contain method’s signature only but not bodies. Methods declared in interface are abstract methods. We can implement many interfaces on a class which support the multiple inheritance. 5) Is it is necessary to implement all methods in an interface? Ans : Yes. All the methods have to be implemented.
6) Which is the default access modifier for an interface method? Ans : public. 7) Can we define a variable in an interface ?and what type it should be ? Ans : Yes we can define a variable in an interface. They are implicitly final and static. 8) What is difference between interface and an abstract class? Ans : All the methods declared inside an Interface are abstract. Where as abstract class must have at least one abstract method and others may be concrete or abstract. In Interface we need not use the keyword abstract for the methods. 9) By default, all program import the java.lang package. True/False Ans : True 10) Java compiler stores the .class files in the path specified in CLASSPATH environmental variable. True/False Ans : False
11) User-defined package can also be imported just like the standard packages. True/False Ans : True 12) When a program does not want to handle exception, the ______class is used. Ans : Throws 13) The main subclass of the Exception class is _______ class. Ans : RuntimeException 14) Only subclasses of ______class may be caught or thrown. Ans : Throwable 15) Any user-defined exception class is a subclass of the _____ class.
Ans : Exception 16) The catch clause of the user-defined exception class should ______ its Base class catch clause. Ans : Exception 17) A _______ is used to separate the hierarchy of the class while declaring an Import statement. Ans : Package
18) All standard classes of Java are included within a package called _____. Ans : java.lang 19) All the classes in a package can be simultaneously imported using ____. Ans : * 20) Can you define a variable inside an Interface. If no, why? If yes, how? Ans.: YES. final and static 21) How many concrete classes can you have inside an interface? Ans.: None 22) Can you extend an interface? Ans.: Yes 23) Is it necessary to implement all the methods of an interface while implementing the interface? Ans.: No 24) If you do not implement all the methods of an interface while implementing , what specifier should you use for the class ? Ans.: abstract 25) How do you achieve multiple inheritance in Java? Ans: Using interfaces. 26) How to declare an interface example?
Ans : access class classname implements interface. 27) Can you achieve multiple interface through interface? a)True b) false Ans : a. 28) Can variables be declared in an interface ? If so, what are the modifiers? Ans : Yes. final and static are the modifiers can be declared in an interface. 29) What are the possible access modifiers when imple menting interface methods? Ans : public. 30) Can anonymous classes be implemented an interface? Ans : Yes. 31) Interfaces can’t be extended. a)True b)False Ans : b. 32) Name interfaces without a method? Ans : Serializable, Cloneble & Remote. 33) Is it possible to use few methods of an interface in a class ? If so, how? Ans : Yes. Declare the class as abstract.
Exception Handling 1) What is the difference between ‘throw’ and ‘throws’ ?And it’s application? Ans : Exceptions that are thrown by java runtime systems can be handled by Try and catch blocks. With throw exception we can handle the exceptions thrown by the program itself. If a method is capable of causing an exception that it does not
handle, it must specify this behavior so the callers of the method can guard against that exception. 2) What is the difference between ‘Exception’ and ‘error’ in java? Ans : Exception and Error are the subclasses of the Throwable class. Exception class is used for exceptional conditions that user program should catch. With exception class we can subclass to create our own custom exception. Error defines exceptions that are not excepted to be caught by you program. Example is Stack Overflow. 3) What is ‘Resource leak’? Ans : Freeing up other resources that might have been allocated at the beginning of a method. 4)What is the ‘finally’ block? Ans : Finally block will execute whether or not an exception is thrown. If an exception is thrown, the finally block will execute even if no catch statement match the exception. Any time a method is about to return to the caller from inside try/catch block, via an uncaught exception or an explicit return statement, the finally clause is also execute. 5) Can we have catch block with out try block? If so when? Ans : No. Try/Catch or Try/finally form a unit. 6) What is the difference between the following statements? Catch (Exception e), Catch (Error err), Catch (Throwable t) Ans :
7) What will happen to the Exception object after exception handling? Ans : It will go for Garbage Collector. And frees the memory.
8) How many Exceptions we can define in ‘throws’ clause? Ans : We can define multiple exceptions in throws clause. Signature is.. type method-name (parameter-list) throws exception-list
9) The finally block is executed when an exception is thrown, even if no catch matches it. True/False Ans : True 10) The subclass exception should precede the base class exception when used within the catch clause. True/False Ans : True 11) Exceptions can be caught or rethrown to a calling method. True/False Ans : True 12) The statements following the throw keyword in a program are not executed. True/False Ans : True 13) The toString ( ) method in the user-defined exception class is overridden. True/False Ans : True
MULTI THREADING 1) What are the two types of multitasking? Ans : 1.process-based 2.Thread-based 2) What are the two ways to create the thread? Ans : 1.by implementing Runnable 2.by extending Thread 3) What is the signature of the constructor of a thread class? Ans : Thread(Runnable threadob,String threadName) 4) What are all the methods available in the Runnable Interface? Ans : run() 5) What is the data type for the method isAlive() and this method is available in which class? Ans : boolean, Thread 6) What are all the methods available in the Thread class? Ans : 1.isAlive() 2.join() 3.resume() 4.suspend()
5.stop() 6.start() 7.sleep() 8.destroy() 7) What are all the methods used for Inter Thread communication and what is the class in which these methods are defined? Ans :1. wait(),notify() & notifyall() 2. Object class 8) What is the mechanisam defind by java for the Resources to be used by only one Thread at a time? Ans : Synchronisation 9) What is the procedure to own the moniter by many threads? Ans : not possible 10) What is the unit for 1000 in the below statement? ob.sleep(1000) Ans : long milliseconds 11) What is the data type for the parameter of the sleep() method? Ans : long 12) What are all the values for the following level? max-priority min-priority normal-priority Ans : 10,1,5 13) What is the method available for setting the priority? Ans : setPriority() 14) What is the default thread at the time of starting the program? Ans : main thread
15) The word synchronized can be used with only a method. True/ False Ans : False 16) Which priority Thread can prompt the lower primary Thread? Ans : Higher Priority 17) How many threads at a time can access a monitor? Ans : one 18) What are all the four states associated in the thread? Ans : 1. new 2. runnable 3. blocked 4. dead 19) The suspend()method is used to teriminate a thread? True /False Ans : False 20) The run() method should necessary exists in clases created as subclass of thread? True /False Ans : True 21) When two threads are waiting on each other and can't proceed the programe is said to be in a deadlock? True/False Ans : True 22) Which method waits for the thread to die ? Ans : join() method
23) Which of the following is true ? 1) wait(),notify(),notifyall() are defined as final & can be called only from with in a synchronized method 2) Among wait(),notify(),notifyall() the wait() method only throws IOException 3) wait(),notify(),notifyall() & sleep() are methods of object class
1 2 3 1&2 1,2 & 3 Ans : D 24) Garbage collector thread belongs to which priority? Ans : low-priority 25) What is meant by timeslicing or time sharing? Ans : Timeslicing is the method of allocating CPU time to individual threads in a priority schedule. 26) What is meant by daemon thread? In java runtime, what is it's role? Ans : Daemon thread is a low priority thread which runs intermittently in the background doing the garbage collection operation for the java runtime system.
Inheritance 1) What is the difference between superclass & subclass? Ans : A super class is a class that is inherited whereas subclass is a class that does the inheriting. 2) Which keyword is used to inherit a class? Ans : extends 3) Subclasses methods can access superclass members/ attributes at all times? True/False Ans : False
4) When can subclasses not access superclass members? Ans : When superclass is declared as private. 5) Which class does begin Java class hierarchy? Ans : Object class 6) Object class is a superclass of all other classes? True/False Ans : True 7) Java supports multiple inheritance? True/False Ans : False 8) What is inheritance? Ans : Deriving an object from an existing class. In the other words, Inheritance is the process of inheriting all the features from a class 9) What are the advantages of inheritance? Ans : Reusability of code and accessibility of variables and methods of the superclass by subclasses. 10) Which method is used to call the constructors of the superclass from the subclass? Ans : super(argument) 11) Which is used to execute any method of the superclass from the subclass? Ans : super.method-name(arguments) 12) Which methods are used to destroy the objects created by the constructor methods? Ans : finalize() 13) What are abstract classes? Ans : Abstract classes are those for which instances can’t be created. 14) What must a class do to implement an interface?
Ans: It must provide all of the methods in the interface and identify the interface in its implements clause. 15) Which methods in the Object class are declared as final? Ans : getClass(), notify(), notifyAll(), and wait() 16) Final methods can be overridden. True/False Ans : False 17) Declaration of methods as final results in faster execution of the program? True/False Ans: True 18) Final variables should be declared in the beginning? True/False Ans : True 19) Can we declare variable inside a method as final variables? Why? Ans : Cannot because, local variable cannot be declared as final variables. 20) Can an abstract class may be final? Ans : An abstract class may not be declared as final. 21) Does a class inherit the constructors of it's super class? Ans: A class does not inherit constructors from any of it's super classes. 22) What restrictions are placed on method overloading? Ans: Two methods may not have the same name and argument list but different return types. 23) What restrictions are placed on method overriding? Ans : Overridden methods must have the same name , argument list , and return type. The overriding method may not limit the access of the method it overridees.The overriding method may not throw any exceptions that may not be thrown by the overridden method.
24) What modifiers may be used with an inner class that is a member of an outer class? Ans : a (non-local) inner class may be declared as public, protected, private, static, final or abstract. 25) How this() is used with constructors? Ans: this() is used to invoke a constructor of the same class 26) How super() used with constructors? Ans : super() is used to invoke a super class constructor 27) Which of the following statements correctly describes an interface? a)It's a concrete class b)It's a superclass c)It's a type of abstract class Ans: c 28) An interface contains __ methods a)Non-abstract b)Implemented c)unimplemented Ans:c
STRING HANDLING Which package does define String and StringBuffer classes? Ans : java.lang package. Which method can be used to obtain the length of the String? Ans : length( ) method. How do you concatenate Strings? Ans : By using " + " operator. Which method can be used to compare two strings for equality? Ans : equals( ) method. Which method can be used to perform a comparison between strings that ignores case differences? Ans : equalsIgnoreCase( ) method. What is the use of valueOf( ) method? Ans : valueOf( ) method converts data from its internal format into a human-readable form. What are the uses of toLowerCase( ) and toUpperCase( ) methods? Ans : The method toLowerCase( ) converts all the characters in a string from uppercase to lowercase. The method toUpperCase( ) converts all the characters in a string from lowercase to uppercase. Which method can be used to find out the total allocated capacity of a StrinBuffer? Ans : capacity( ) method. Which method can be used to set the length of the buffer within a StringBuffer object? Ans : setLength( ). What is the difference between String and StringBuffer? Ans : String objects are constants, whereas StringBuffer objects are not.
String class supports constant strings, whereas StringBuffer class supports growable, modifiable strings. What are wrapper classes? Ans : Wrapper classes are classes that allow primitive types to be accessed as objects. Which of the following is not a wrapper class? String Integer Boolean Character Ans : a. What is the output of the following program? public class Question { public static void main(String args[]) { String s1 = "abc"; String s2 = "def"; String s3 = s1.concat(s2.toUpperCase( ) ); System.out.println(s1+s2+s3); } } abcdefabcdef abcabcDEFDEF abcdefabcDEF None of the above ANS : c. Which of the following methods are methods of the String class? delete( )
append( ) reverse( ) replace( ) Ans : d. Which of the following methods cause the String object referenced by s to be changed? s.concat( ) s.toUpperCase( ) s.replace( ) s.valueOf( ) Ans : a and b. String is a wrapper class? True False Ans : b. 17) If you run the code below, what gets printed out? String s=new String("Bicycle");
int iBegin=1;
char iEnd=3;
System.out.println(s.substring(iBegin,iEnd)); Bic ic c) icy d) error: no method matching substring(int,char)
Ans : b. 18) Given the following declarations String s1=new String("Hello")
String s2=new String("there");
String s3=new String(); Which of the following are legal operations? s3=s1 + s2; s3=s1 - s2; c) s3=s1 & s2 d) s3=s1 && s2 Ans : a. 19) Which of the following statements are true? The String class is implemented as a char array, elements are addressed using the stringname[] convention b) Strings are a primitive type in Java that overloads the + operator for concatenation c) Strings are a primitive type in Java and the StringBuffer is used as the matching wrapper type d) The size of a string can be retrieved using the length property. Ans : b.
EXPLORING JAVA.LANG java.lang package is automatically imported into all programs. True
False Ans : a What are the interfaces defined by java.lang? Ans : Cloneable, Comparable and Runnable. What are the constants defined by both Flaot and Double classes? Ans : MAX_VALUE, MIN_VALUE, NaN, POSITIVE_INFINITY, NEGATIVE_INFINITY and TYPE. What are the constants defined by Byte, Short, Integer and Long? Ans : MAX_VALUE, MIN_VALUE and TYPE. What are the constants defined by both Float and Double classes? Ans : MAX_RADIX, MIN_RADIX, MAX_VALUE, MIN_VALUE and TYPE. What is the purpose of the Runtime class? Ans : The purpose of the Runtime class is to provide access to the Java runtime system. What is the purpose of the System class? Ans : The purpose of the System class is to provide access to system resources.
Which class is extended by all other classes? Ans : Object class is extended by all other classes. Which class can be used to obtain design information about an object? Ans : The Class class can be used to obtain information about an object’s design. Which method is used to calculate the absolute value of a number? Ans : abs( ) method. What are E and PI? Ans : E is the base of the natural logarithm and PI is the mathematical value pi. Which of the following classes is used to perform basic console I/O? System SecurityManager Math Runtime Ans : a. Which of the following are true? The Class class is the superclass of the Object class. The Object class is final. The Class class can be used to load other classes. The ClassLoader class can be used to load other classes. Ans : c and d. Which of the following methods are methods of the Math class? absolute( ) log( ) cosine( ) sine( ) Ans : b.
Which of the following are true about the Error and Exception classes? Both classes extend Throwable. The Error class is final and the Exception class is not. The Exception class is final and the Error is not. Both classes implement Throwable. Ans : a. Which of the following are true? The Void class extends the Class class. The Float class extends the Double class. The System class extends the Runtime class. The Integer class extends the Number class. Ans : d.
17) Which of the following will output -4.0 System.out.println(Math.floor(-4.7)); System.out.println(Math.round(-4.7)); System.out.println(Math.ceil(-4.7)); d) System.out.println(Math.Min(-4.7)); Ans : c. 18) Which of the following are valid statements a) public class MyCalc extends Math b) Math.max(s); c) Math.round(9.99,1); d) Math.mod(4,10);
e) None of the above. Ans : e. 19) What will happen if you attempt to compile and run the following code? Integer ten=new Integer(10);
Long nine=new Long (9);
System.out.println(ten + nine);
int i=1;
System.out.println(i + ten); 19 followed by 20 19 followed by 11 Error: Can't convert java lang Integer d) 10 followed by 1 Ans : c.
INPUT / OUTPUT : EXPLORING JAVA.IO What is meant by Stream and what are the types of Streams and classes of the Streams? Ans : A Stream is an abstraction that either produces or consumes information. There are two types of Streams. They are: Byte Streams : Byte Streams provide a convenient means for handling input and output of bytes. Character Streams : Character Streams provide a convenient means for handling input and output of characters.
Byte Stream classes : Byte Streams are defined by using two abstract classes. They are:InputStream and OutputStream. Character Stream classes : Character Streams are defined by using two abstract classes. They are : Reader and Writer. Which of the following statements are true? UTF characters are all 8-bits. UTF characters are all 16-bits. UTF characters are all 24-bits. Unicode characters are all 16-bits. Bytecode characters are all 16-bits. Ans : d. Which of the following statements are true? When you construct an instance of File, if you do not use the filenaming semantics of the local machine, the constructor will throw an IOException. When you construct an instance of File, if the corresponding fi le does not exist on the local file system, one will be created. When an instance of File is garbage collected, the corresponding file on the local file system is deleted. None of the above. Ans : a,b and c. The File class contains a method that changes the current working directory. True False Ans : b. It is possible to use the File class to list the contents of the current working directory. True False Ans : a.
Readers have methods that can read and return floats and doubles. True False Ans : b. You execute the code below in an empty directory. What is the result? File f1 = new File("dirname"); File f2 = new File(f1, "filename"); A new directory called dirname is created in the current working directory. A new directory called dirname is created in the current working directory. A new file called filename is created in directory dirname. A new directory called dirname and a new file called filename are created, both in the current working directory. A new file called filename is created in the current working directory. No directory is created, and no file is created. Ans : e. What is the difference between the Reader/Writer class hierarchy and the InputStream/OutputStream class hierarchy? Ans : The Reader/Writer class hierarchy is character-oriented and the InputStream/OutputStream class hierarchy is byte -oriented. What is an I/O filter? Ans : An I/O filter is an object that reads from one stream and writes to another, usually altering the data in some way as it is passed from one stream to another. What is the purpose of the File class? Ans : The File class is used to create objects that provide access to the files and directories of a local file system. What interface must an object implement before it can be written to a stream as an object? Ans : An object must implement the Serializable or Externalizable interface before it can be written to a stream as an object.
What is the difference between the File and RandomAccessFile classes? Ans : The File class encapsulates the files and directories of the local file system. The RandomAccessFile class provides the methods needed to directly access data contained in any part of a file. What class allows you to read objects directly from a stre am? Ans : The ObjectInputStream class supports the reading of objects from input streams. What value does read( ) return when it has reached the end of a file? Ans : The read( ) method returns – 1 when it has reached the end of a file. What value does readLine( ) return when it has reached the end of a file? Ans : The readLine( ) method returns null when it has reached the end of a file. How many bits are used to represent Unicode, ASCII, UTF-16 and UTF-8 characters? Ans : Unicode requires 16-bits and ASCII requires 8-bits. Although the ASCII character set uses only 1-bits, it is usually represented as 8-bits. UTF-8 represents characters using 8, 16 and 18-bit patterns. UTF-16 uses 16-bit and larger bit patterns. Which of the following are true? The InputStream and OutputStream classes are byte -oriented. The ObjectInputStream and ObjectOutputStream do not support serialized object input and output. The Reader and Writer classes are character-oriented. The Reader and Writer classes are the preferred solution to serialized object output. Ans : a and c. Which of the following are true about I/O filters? Filters are supported on input, but not on output. Filters are supported by the InputStream/OutputStream class hierarchy, but not by the Reader/Writer class hierarchy. Filters read from one stream and write to another. A filter may alter data that is read from one stream and written to another.
Ans : c and d. Which of the following are true? Any Unicode character is represented using 16-bits. 7-bits are needed to represent any ASCII character. UTF-8 characters are represented using only 8-bits. UTF-16 characters are represented using only 16-bits. Ans : a and b. Which of the following are true? The Serializable interface is used to identify objects that may be written to an output stream. The Externalizable interface is implemented by classes that control the way in which their objects are serialized. The Serializable interface extends the Externalizable interface. The Externalizable interface extends the Serializable interface. Ans : a, b and d. Which of the following are true about the File class? A File object can be used to change the current working directory. A File object can be used to access the files in the current directory. When a File object is created, a corresponding directory or file is created in the local file system. File objects are used to access files and directories on the local file system. File objects can be garbage collected. When a File object is garbage colle cted, the corresponding file or directory is deleted. Ans : b, d and e. How do you create a Reader object from an InputStream object? Use the static createReader( ) method of InputStream class. Use the static createReader( ) method of Reader class.
Create an InputStreamReader object, passing the InputStream object as an argument to the InputStreamReader constructor. Create an OutputStreamReader object, passing the InputStream object as an argument to the OutputStreamReader constructor. Ans : c. Which of the following are true? Writer classes can be used to write characters to output streams using different character encodings. Writer classes can be used to write Unicode characters to output streams. Writer classes have methods that support the writing of the values of any Java primitive type to output streams. Writer classes have methods that support the writing of objects to output streams. Ans : a and b. The isFile( ) method returns a boolean value depending on whether the file object is a file or a directory. True. False. Ans : a. Reading or writing can be done even after closing the input/output source. True. False. Ans : b.
The ________ method helps in clearing the buffer. Ans : flush( ). The System.err method is used to print error message. True. False.
Ans : a. What is meant by StreamTokenizer? Ans : StreamTokenizer breaks up InputStream into tokens that are delimited by sets of characters. It has the constructor : StreamTokenizer(Reader inStream). Here inStream must be some form of Reader. What is Serialization and deserialization? Ans : Serialization is the process of writing the state of an object to a byte stream. Deserialization is the process of restoring these objects. 30) Which of the following can you perform using the File class? a) Change the current directory b) Return the name of the parent directory c) Delete a file d) Find if a file contains text or binary information Ans : b and c. 31)How can you change the current working directory using an instance of the File class called FileName? FileName.chdir("DirName"). FileName.cd("DirName"). FileName.cwd("DirName"). The File class does not support directly changing the current directory. Ans : d.
EVENT HANDLING
The event delegation model, introduced in release 1.1 of the JDK, is fully compatible with the event model. True False Ans : b. A component subclass that has executed enableEvents( ) to enable processing of a certain kind of event cannot also use an adapter as a listener for the same kind of event. True False Ans : b. What is the highest-level event class of the event-delegation model? Ans : The java.util.eventObject class is the highest-level class in the event-delegation hierarchy. What interface is extended by AWT event listeners? Ans : All AWT event listeners extend the java.util.EventListener interface. What class is the top of the AWT event hierarchy? Ans : The java.awt.AWTEvent class is the highest-level class in the AWT event class hierarchy. What event results from the clicking of a button? Ans : The ActionEvent event is generated as the result of the clicking of a butt on. What is the relationship between an event-listener interface and an event-adapter class? Ans : An event-listener interface defines the methods that must be implemented by an event handler for a particular kind of event. An event adapter provides a de fault implementation of an event-listener interface.
In which package are most of the AWT events that support the event-delegation model defined? Ans : Most of the AWT–related events of the event-delegation model are defined in the java.awt.event package. The AWTEvent class is defined in the java.awt package. What is the advantage of the event-delegation model over the earlier event-inheritance model? Ans : The event-delegation has two advantages over the event-inheritance model. The y are : It enables event handling by objects other than the ones that generate the events. This allows a clean separation between a component’s design and its use. It performs much better in applications where many events are generated. This performance improvement is due to the fact that the event-delegation model does not have to repeatedly process unhandled events, as is the case of the event -inheritance model. What is the purpose of the enableEvents( ) method? Ans :The enableEvents( ) method is used to enable an event for a particular object. Which of the following are true? The event-inheritance model has replaced the event-delegation model. The event-inheritance model is more efficient than the event-delegation model. The event-delegation model uses event listeners to define the methods of eventhandling classes. The event-delegation model uses the handleEvent( ) method to support event handling. Ans : c. Which of the following is the highest class in the event-delegation model? java.util.EventListener java.util.EventObject java.awt.AWTEvent java.awt.event.AWTEvent
Ans : b. When two or more objects are added as listeners for the same event, which listener is first invoked to handle the event? The first object that was added as listener. The last object that was added as listener. There is no way to determine which listener will be invoked first. It is impossible to have more than one listener for a given event. Ans : c. Which of the following components generate action events? Buttons Labels Check boxes Windows Ans : a. Which of the following are true? A TextField object may generate an ActionEvent. A TextArea object may generate an ActionEvent. A Button object may generate an ActionEvent. A MenuItem object may generate an ActionEvent. Ans : a,c and d. Which of the following are true? The MouseListener interface defines methods for handling mouse clicks. The MouseMotionListener interface defines methods for handling mouse clicks. The MouseClickListener interface defines methods for handling mouse clicks. The ActionListener interface defines methods for handling the clicking of a button. Ans : a and d.
Suppose that you want to have an object eh handle the TextEvent of a TextArea object t. How should you add eh as the event handler for t? t.addTextListener(eh); eh.addTextListener(t); addTextListener(eh.t); addTextListener(t,eh); Ans : a. What is the preferred way to handle an object’s events in Java 2? Override the object’s handleEvent( ) method. Add one or more event listeners to handle the events. Have the object override its processEvent( ) methods. Have the object override its dispatchEvent( ) methods. Ans : b. Which of the following are true? A component may handle its own events by adding itself as an event listener. A component may handle its own events by overriding its event-dispatching method. A component may not handle oits own events. A component may handle its own events only if it implements the handleEvent( ) method. Ans : a and b.
APPLETS What is an Applet? Should applets have constructors? Ans : Applet is a dynamic and interactive program that runs inside a Web page displayed by a Java capable browser. We don’t have the concept of Constructors in Applets. How do we read number information from my applet’s parameters, given that Applet’s getParameter() method returns a string? Ans : Use the parseInt() method in the Integer Class, the Float(String) constructor in the Class Float, or the Double(String) constructor in the class Double. How can I arrange for different applets on a web page to communicate with each other? Ans : Name your applets inside the Applet tag and invoke AppletContext’s getApplet() method in your applet code to obtain references to the other applets on the page. How do I select a URL from my Applet and send the browser to that page?
Ans : Ask the applet for its applet context and invoke showDocument() on that context object. Eg. URL targetURL; String URLString AppletContext context = ge tAppletContext(); try{ targetUR L = new URL(URLString); } catch (Malformed URLException e){ // Code for recover from the exception } context. showDocument (targetURL); Can applets on different pages communicate with each other? Ans : No. Not Directly. The applets will exchange the information at one meeting place either on the local file system or at remote system. How do Applets differ from Applications? Ans : Appln: Stand Alone Applet: Needs no explicit installation on local m/c. Appln: Execution starts with main() method. Applet: Execution starts with init() method. Appln: May or may not be a GUI Applet: Must run within a GUI (Using AWT) How do I determine the width and height of my application? Ans : Use the getSize() method, which the Applet class inherits from the Component class in the Java.awt package. The getSize() method returns the size of the applet as a Dimension object, from which you extract separate width, height fields. Eg. Dimension dim = getSize ();
int appletwidth = dim.width (); 8) What is AppletStub Interface? Ans : The applet stub interface provides the means by which an applet and the browser communicate. Your code will not typically implement this interface. It is essential to have both the .java file and the .html file of an applet in the same directory. True. False. Ans : b. The tag contains two attributes namely _________ and _______. Ans : Name , value.
Passing values to parameters is done in the _________ file of an applet. Ans : .html. 12) What tags are mandatory when creating HTML to display an applet name, height, width code, name codebase, height, width d) code, height, width Ans : d. Applet’s getParameter( ) method can be used to get parameter value s. True. False. Ans : a. What are the Applet’s Life Cycle methods? Explain them? Ans : init( ) method - Can be called when an applet is first loaded.
start( ) method - Can be called each time an applet is started. paint( ) method - Can be called when the applet is minimized or refreshed. stop( ) method - Can be called when the browser moves off the applet’s page. destroy( ) method - Can be called when the browser is finished with the applet. What are the Applet’s information methods? Ans : getAppletInfo( ) method : Returns a string describing the applet, its author ,copy right information, etc. getParameterInfo( ) method : Returns an array of string describing the applet’s parameters. All Applets are subclasses of Applet. True. False. Ans : a. All Applets must import java.applet and java.awt. True. False. Ans : a. What are the steps involved in Applet development? Ans : a) Edit a Java source file, b) Compile your program and c) Execute the appletviewer, specifying the name of your applet’s source file. Applets are executed by the console based Java run-time interpreter. True. False. Ans : b. Which classes and interfaces does Applet class consist?
Ans : Applet class consists of a single class, the Applet class a nd three interfaces: AppletContext, AppletStub and AudioClip. What is the sequence for calling the methods by AWT for applets? Ans : When an applet begins, the AWT calls the following methods, in this sequence. init( ) start( ) paint( ) When an applet is terminated, the following sequence of method cals takes place : stop( ) destroy( ) Which method is used to output a string to an applet? Ans : drawString ( ) method. Every color is created from an RGB value. True. False Ans : a.
AWT : WINDOWS, GRAPHICS AND FONTS How would you set the color of a graphics context called g to cyan? g.setColor(Color.cyan); g.setCurrentColor(cyan); g.setColor("Color.cyan"); g.setColor("cyan’); g.setColor(new Color(cyan));
Ans : a. The code below draws a line. What color is the line? g.setColor(Color.red.green.yellow.red.cyan); g.drawLine(0, 0, 100,100); Red Green Yellow Cyan Black Ans : d. What does the following code draw? g.setColor(Color.black); g.drawLine(10, 10, 10, 50); g.setColor(Color.RED); g.drawRect(100, 100, 150, 150); A red vertical line that is 40 pixels long and a red square with sides of 150 pixels A black vertical line that is 40 pixels long and a red square with sides of 150 pixels A black vertical line that is 50 pixels long and a red square with sides of 150 pixels A red vertical line that is 50 pixels long and a red square with sides of 150 pixels A black vertical line that is 40 pixels long and a red square with sides of 100 pixel Ans : b. Which of the statements below are true? A polyline is always filled. b) A polyline can not be filled. c) A polygon is always filled. d) A polygon is always closed
e) A polygon may be filled or not filled Ans : b, d and e. What code would you use to construct a 24-point bold serif font? new Font(Font.SERIF, 24,Font.BOLD); new Font("SERIF", 24, BOLD"); new Font("BOLD ", 24,Font.SERIF); new Font("SERIF", Font.BOLD,24); new Font(Font.SERIF, "BOLD", 24); Ans : d. What does the following paint( ) method draw? Public void paint(Graphics g) { g.drawString("question #6",10,0); } The string "question #6", with its top-left corner at 10,0 A little squiggle coming down from the top of the component, a little way in from the left edge Ans : b.
What does the following paint( ) method draw? Public void paint(Graphics g) { g.drawString("question #6",10,0); } A circle at (100, 100) with radius of 44 A circle at (100, 44) with radius of 100 A circle at (100, 44) with radius of 44
The code does not compile Ans : d. 8)What is relationship between the Canvas class and the Graphics class? Ans : A Canvas object provides access to a Graphics object via its paint( ) method. What are the Component subclasses that support painting. Ans : The Canvas, Frame, Panel and Applet classes support painting. What is the difference between the paint( ) and repaint( ) method? Ans : The paint( ) method supports painting via a Graphics object. The repaint( ) method is used to cause paint( ) to be invoked by the AWT painting method. What is the difference between the Font and FontMetrics classes? Ans : The FontMetrics class is used to define implementation-specific properties, such as ascent and descent, of a Font object. Which of the following are passed as an argument to the paint( ) method? A Canvas object A Graphics object An Image object A paint object Ans : b. Which of the following methods are invoked by the AWT to support paint and repaint operations? paint( ) repaint( ) draw( ) redraw( ) Ans : a.
Which of the following classes have a paint( ) method? Canvas Image Frame Graphics Ans : a and c. Which of the following are methods of the Graphics class? drawRect( ) drawImage( ) drawPoint( ) drawString( ) Ans : a, b and d. Which Font attributes are available through the FontMetrics class? ascent leading case height Ans : a, b and d. Which of the following are true? The AWT automatically causes a window to be repainted when a portion of a window has been minimized and then maximized. The AWT automatically causes a window to be repainted when a portion of a window has been covered and then uncovered. The AWT automatically causes a window to be repainted when application data is changed. The AWT does not support repainting operations. Ans : a and b.
Which method is used to size a graphics object to fit the current size of the window? Ans : getSize( ) method. What are the methods to be used to set foreground and background colors? Ans : setForeground( ) and setBackground( ) methods. 19) You have created a simple Frame and overridden the paint method as follows public void paint(Graphics g){
g.drawString("Dolly",50,10);
} What will be the result when you attempt to compile and run the program? The string "Dolly" will be displayed at the centre of the frame b) An error at compilation complaining at the signature of the paint method c) The lower part of the word Dolly will be seen at the top of the form, with the top hidden. d) The string "Dolly" will be shown at the bottom of the form Ans : c. 20) Where g is a graphics instance what will the following code draw on the screen. g.fillArc(45,90,50,50,90,180); a) An arc bounded by a box of height 45, width 90 with a centre point of 50,50, starting at an angle of 90 degrees traversing through 180 degrees counter clockwise. b) An arc bounded by a box of height 50, width 50, with a centre point of 45,90 starting at an angle of 90 degrees traversing through 180 degrees clockwise. c) An arc bounded by a box of height 50, width 50, with a top left at coordinates of 45, 90, starting at 90 degrees and traversing through 180 degrees counter clockwise.
d) An arc starting at 45 degrees, traversing through 90 degrees clockwise bounded by a box of height 50, width 50 with a centre point of 90, 180. Ans : c. 21) Given the following code import java.awt.*; public class SetF extends Frame{ public static void main(String argv[]){ SetF s = new SetF(); s.setSize(300,200); s.setVisible(true); } } How could you set the frame surface color to pink a)s.setBackground(Color.pink); b)s.setColor(PINK); c)s.Background(pink); d)s.color=Color.pink Ans : a.
AWT: CONTROLS, LAYOUT MANAGERS AND MENUS What is meant by Controls and what are different types of controls? Ans : Controls are componenets that allow a user to interact with your application.
The AWT supports the following types of controls: Labels Push buttons Check boxes Choice lists Lists Scroll bars Text components These controls are subclasses of Component. You want to construct a text area that is 80 character-widths wide and 10 characterheights tall. What code do you use? new TextArea(80, 10) new TextArea(10, 80) Ans: b. A text field has a variable -width font. It is constructed by calling new TextField("iiiii"). What happens if you change the contents of the text field to "wwwww"? (Bear in mind that is one of the narrowest characters, and w is one of the widest.) The text field becomes wider. The text field becomes narrower. The text field stays the same width; to see the entire contents you will have to scroll by using the ß and à keys. The text field stays the same width; to see the entire contents you will have to scroll by using the text field’s horizontal scroll bar. Ans : c. The CheckboxGroup class is a subclass of the Component class. True False
Ans : b. 5) What are the immediate super classes of the following classes? a) Container class b) MenuComponent class c) Dialog class d) Applet class e) Menu class Ans : a) Container - Component b) MenuComponent - Object c) Dialog - Window d) Applet - Panel e) Menu - MenuItem 6) What are the SubClass of Textcomponent Class? Ans : TextField and TextArea 7) Which method of the component class is used to set the position and the size of a component? Ans : setBounds() 8) Which TextComponent method is used to set a TextComponent to the read-only state? Ans : setEditable() 9) How can the Checkbox class be used to create a radio button? Ans : By associating Checkbox objects with a CheckboxGroup. 10) What Checkbox method allows you to tell if a Checkbox is checked? Ans : getState() 11) Which Component method is used to access a component's immediate Container? getVisible() getImmediate
getParent() getContainer Ans : c. 12) What methods are used to get and set the text label displayed by a Button object? Ans : getLabel( ) and setLabel( ) 13) What is the difference between a Choice and a List? Ans : A Choice is displayed in a compact form that requires you to pull it down to see the list of available choices. Only one item may be selected from a Choice. A List may be displayed in such a way that several List items are visible. A List supports the selection of one or more List items. 14) Which Container method is used to cause a container to be laid out and redisplayed? Ans : validate( ) 15) What is the difference between a Scollbar and a Scrollpane? Ans : A Scrollbar is a Component, but not a Container. A Scrollpane is a Container and handles its own events and performs its own scrolling. 16) Which Component subclass is used for drawing and painting? Ans : Canvas. 17) Which of the following are direct or indirect subclasses of Component? Button Label CheckboxMenuItem Toolbar Frame Ans : a, b and e. 18) Which of the following are direct or indirect subclasses of Container?
Frame TextArea MenuBar FileDialog Applet Ans : a,d and e. 19) Which method is used to set the text of a Label object? setText( ) setLabel( ) setTextLabel( ) setLabelText( ) Ans : a. 20) Which constructor creates a TextArea with 10 rows and 20 columns? new TextArea(10, 20) new TextArea(20, 10) new TextArea(new Rows(10), new columns(20)) new TextArea(200) Ans : a. (Usage is TextArea(rows, columns) 21) Which of the following creates a List with 5 visible items and multiple selection enabled? new List(5, true) new List(true, 5) new List(5, false) new List(false,5) Ans : a.
[Usage is List(rows, multipleMode)] 22) Which are true about the Container class? The validate( ) method is used to cause a Container to be laid out and redisplayed. The add( ) method is used to add a Component to a Container. The getBorder( ) method returns information about a Container’s insets. The getComponent( ) method is used to access a Component that is contained in a Container. Ans : a, b and d. 23) Suppose a Panel is added to a Frame and a Button is added to the Panel. If the Frame’s font is set to 12-point TimesRoman, the Panel’s font is set to 10-point TimesRoman, and the Button’s font is not set, what font will be used to dispaly the Button’s label? 12-point TimesRoman 11-point TimesRoman 10-point TimesRoman 9-point TimesRoman Ans : c. A Frame’s background color is set to Color.Yellow, and a Button’s background color is to Color.Blue. Suppose the Button is added to a Panel, which is added to the Frame. What background color will be used with the Panel? Colr.Yellow Color.Blue Color.Green Color.White Ans : a. 25) Which method will cause a Frame to be displayed? show( ) setVisible( )
display( ) displayFrame( ) Ans : a and b. 26) All the componenet classes and container classes are derived from _________ class. Ans : Object. 27) Which method of the container class can be used to add components to a Panel. Ans : add ( ) method. 28) What are the subclasses of the Container class? Ans : The Container class has three major subclasses. They are : Window Panel ScrollPane 29) The Choice component allows multiple selection. True. False. Ans : b. 30) The List component does not generate any events. True. False. Ans : b. 31) Which components are used to get text input from the user. Ans : TextField and TextArea. 32) Which object is needed to group Checkboxes to make them exclusive? Ans : CheckboxGroup. 33) Which of the following components allow multiple selections? Non-exclusive Checkboxes.
Radio buttons. Choice. List. Ans : a and d. 34) What are the types of Checkboxes and what is the difference between them? Ans : Java supports two types of Checkboxes. They are : Exclusive and Non-exclusive. In case of exclusive Checkboxes, only one among a group of items can be selected at a time. I f an item from the group is selected, the checkbox currently checked is deselected and the new selection is highlighted. The exclusive Checkboxes are also called as Radio buttons. The non-exclusive checkboxes are not grouped together and each one can be selected independent of the other. 35) What is a Layout Manager and what are the different Layout Managers available in java.awt and what is the default Layout manager for the panal and the panal subclasses? Ans: A layout Manager is an object that is used to organize components in a container. The different layouts available in java.awt are : FlowLayout, BorderLayout, CardLayout, GridLayout and GridBag Layout. The default Layout Manager of Panal and Panal sub classes is FlowLayout". 36) Can I exert control over the size and placement of components in my interface? Ans : Yes. myPanal.setLayout(null); myPanal.setbounds(20,20,200,200); 37) Can I add the same component to more than one container? Ans : No. Adding a component to a container automatically remove s it from any previous parent(container). 38) How do I specify where a window is to be placed? Ans : Use setBounds, setSize, or setLocation methods to implement this. setBounds(int x, int y, int width, int height)
setBounds(Rectangle r) setSize(int width, int height) setSize(Dimension d) setLocation(int x, int y) setLocation(Point p)
39) How can we create a borderless window? Ans : Create an instance of the Window class, give it a size, and show it on the screen. eg. Frame aFrame = ...... Window aWindow = new Window(aFrame); aWindow.setLayout(new FlowLayout()); aWindow.add(new Button("Press Me")); aWindow.getBounds(50,50,200,200); aWindow.show();
40) Can I create a non-resizable windows? If so, how? Ans: Yes. By using setResizable() method in class Frame. 41) What is the default Layout Manager for the Window and Window subclasses (Frame,Dialog)? Ans : BorderLayout(). 42) How are the elements of different layouts organized? Ans : FlowLayout : The elements of a FlowLayout are organized in a top to bottom, left to right fashion. BorderLayout : The elements of a BorderLayout are organized at the borders (North, South, East and West) and the center of a container.
CardLayout : The elements of a CardLayout are stacked, one on top of the other, like a deck of cards. GridLayout : The elements of a GridLayout are of equal size and are laid out using the square of a grid. GridBagLayout : The elements of a GridBagLayout are organized according to a grid.However, the elements are of different sizes and may occupy more than one row or column of the grid. In addition, the rows and columns may have different sizes. 43) Which containers use a BorderLayout as their default layout? Ans : The Window, Frame and Dialog classes use a BorderLayout as their default layout.
44) Which containers use a FlowLayout as their default layout? Ans : The Panel and the Applet classes use the FlowLayout as their default layout. 45) What is the preferred size of a component? Ans : The preferred size of a component size that will allow the component to display normally. 46) Which method is method to set the layout of a container? startLayout( ) initLayout( ) layoutContainer( ) setLayout( ) Ans : d. 47) Which method returns the preferred size of a component? getPreferredSize( ) getPreferred( ) getRequiredSize( ) getLayout( )
Ans : a.
48) Which layout should you use to organize the components of a container in a tabular form? CardLayout BorederLayout FlowLayout GridLayout Ans : d. An application has a frame that uses a Border layout manager. Why is it probably not a good idea to put a vertical scroll bar at North in the frame? The scroll bar’s height would be its preferred height, which is not likely to be enough. The scroll bar’s width would be the entire width of the frame, which would be much wider than necessary. Both a and b. Neither a nor b. There is no problem with the layout as described. Ans : c. What is the default layouts for a applet, a frame and a panel? Ans : For an applet and a panel, Flow layout is the default layout, whereas Border layout is default layout for a frame. If a frame uses a Grid layout manager and does not contain any panels, then all the components within the frame are the same width and height. True False.
Ans : a. If a frame uses its default layout manager and does not contain any panels, then all the components within the frame are the same width and height. True False. Ans : b. With a Border layout manager, the component at Center gets all the space that is left over, after the components at North and South have been considered. True False Ans : b. An Applet has its Layout Manager set to the default of FlowLayout. What code woul d be the correct to change to another Layout Manager? setLayoutManager(new GridLayout()); setLayout(new GridLayout(2,2)); c) setGridLayout(2,2,)) d setBorderLayout(); Ans : b. 55) How do you indicate where a component will be positioned using Flowlayout? a) North, South,East,West b) Assign a row/column grid reference c) Pass a X/Y percentage parameter to the add method d) Do nothing, the FlowLayout will position the component Ans :d.
56) How do you change the current layout manager for a containe r? a) Use the setLayout method b) Once created you cannot change the current layout manager of a component c) Use the setLayoutManager method d) Use the updateLayout method Ans :a. 57)When using the GridBagLayout manager, each new component requires a new instance of the GridBagConstraints class. Is this statement true or false? a) true b) false Ans : b. 58) Which of the following statements are true? a)The default layout manager for an Applet is FlowLayout b) The default layout manager for an application is FlowLayout c) A layout manager must be assigned to an Applet before the setSize method is called d) The FlowLayout manager attempts to honor the preferred size of any components Ans : a and d. 59) Which method does display the messages whenever there is an item selection or deselection of the CheckboxMenuItem menu? Ans : itemStateChanged method. 60) Which is a dual state menu item? Ans : CheckboxMenuItem. 61) Which method can be used to enable/diable a checkbox menu item? Ans : setState(boolean). Which of the following may a menu contain? A separator A check box
A menu A button A panel Ans : a and c. Which of the following may contain a menu bar? A panel A frame An applet A menu bar A menu Ans : b 64) What is the difference between a MenuItem and a CheckboxMenuItem? Ans : The CheckboxMenuItem class extends the MenuItem class to support a menu item that may be checked or unchecked.
65) Which of the following are true? A Dialog can have a MenuBar. MenuItem extends Menu. A MenuItem can be added to a Menu. A Menu can be added to a Menu. Ans : c and d.
Which colour is used to indicate instance methods in the standard "javadoc" format documentation: 1) blue
2) red 3) purple 4) orange Answer : 2 explain In JDK 1.1 the variabels, methods and constructors are colour coded to simplifytheir identification. endExplain What is the correct ordering for the import, class and package declarations when found in a single file? 1) package, import, class 2) class, import, package 3) import, package, class 4) package, class, import Answer : 1 explain This is my explanation for question 2 endExplain Which methods can be legally applied to a string object? (Multiple) 1) equals(String) 2) equals(Object) 3) trim() 4) round() 5) toString() Answer : 1,2,3,5 What is the parameter specification for the public static void main method?
(multiple) 1) String args [] 2) String [] args 3) Strings args [] 4) String args Answer : 1,2 What does the zeroth element of the string array passed to the public static void main method contain? (multiple) 1) The name of the program 2) The number of arguments 3) The first argument if one is present Answer : 3 Which of the following are Java keywords? (multiple) 1) goto 2) malloc 3) extends 4) FALSE Answer : 3 What will be the result of compiling the following code: public class Test { public static void main (String args []) { int age; age = age + 1; System.out.println("The age is " + age);
} } 1) Compiles and runs with no output 2) Compiles and runs printing out The age is 1 3) Compiles but generates a runtime error 4) Does not compile 5) Compiles but generates a compile time error Answer : 4 Which of these is the correct format to use to create the literal char value a? (multiple) 1) 'a' 2) "a" 3) new Character(a) 4) \000a Answer : 1 What is the legal range of a byte integral type? 1) 0 - 65, 535 2) (-128) - 127 3) (-32,768) - 32,767 4) (-256) - 255 Answer : 2 Which of the following is illegal: 1) int i = 32; 2) float f = 45.0; 3) double d = 45.0; Answer 2
What will be the result of compiling the following code: public class Test { static int age; public static void main (String args []) { age = age + 1; System.out.println("The age is " + age); } } 1) Compiles and runs with no output 2) Compiles and runs printing out The age is 1 3) Compiles but generates a runtime error 4) Does not compile 5) Compiles but generates a compile time error Answer : 2 Which of the following are correct? (multiple) 1) 128 >> 1 gives 64 2) 128 >>> 1 gives 64 3) 128 >> 1 gives -64 4) 128 >>> 1 gives -64 Answer : 1 Which of the following return true? (multiple) 1) "john" == new String("john") 2) "john".equals("john") 3) "john" = "john"
4) "john".equals(new Button("john")) Answer : 2 Which of the following do not lead to a runtime error? (multiple) 1) "john" + " was " + " here" 2) "john" + 3 3) 3 + 5 4) 5 + 5.5 answer 1,2,3,4 Which of the following are so called "short circuit" logical operators? (multiple) 1) & 2) || 3) && 4) | Answer : 2,3 Which of the following are acceptable? (multiple) 1) Object o = new Button("A"); 2) Boolean flag = true; 3) Panel p = new Frame(); 4) Frame f = new Panel(); 5) Panel p = new Apple t(); Answer : 1,5 What is the result of compiling and running the following code: public class Test {
static int total = 10; public static void main (String args []) { new Test(); } public Test () { System.out.println("In test"); System.out.println(this); int temp = this.total; if (temp > 5) { System.out.println(temp); } } } (multiple) 1) The class will not compile 2) The compiler reports and error at line 2 3) The compiler reports an error at line 9 4) The value 10 is one of the e lements printed to the standard output 5) The class compiles but generates a runtime error Answer : 4 Which of the following is correct: 1) String temp [] = new String {"j" "a" "z"}; 2) String temp [] = { "j " " b" "c"}; 3) String temp = {"a", "b", "c"}; 4) String temp [] = {"a", "b", "c"}; Answer 4
What is the correct declaration of an abstract method that is intended to be public: 1) public abstract void add(); 2) public abstract void add() {} 3) public abstract add(); 4) public virtual add(); Answer : 1 Under what situations do you obtain a default constructor? 1) When you define any class 2) When the class has no other constructors 3) When you define at least one constructor Answer : 2 Which of the following can be used to define a constructor for this class, given the following code: public class Test { ... } 1) public void Test() {...} 2) public Test() {...} 3) public static Test() {...} 4) public static void Test() {...} Answer : 2 Which of the following are acceptable to the Java compiler: (multiple) 1) if (2 == 3) System.out.println("Hi"); 2) if (2 = 3) System.out.println("Hi"); 3) if (true) System.out.println("Hi");
4) if (2 != 3) System.out.println("Hi"); 5) if (aString.equals("hello")) System.out.println("Hi"); Answer : 1,3,4,5 Assuming a method contains code which may raise an Exception (but not a RuntimeException), what is the correct way for a method to indicate that it expects the caller to handle that exception: 1) throw Exception 2) throws Exception 3) new Exception 4) Don't need to specify anything Answer : 2 What is the result of executing the following code, using the parameters 4 and 0: public void divide(int a, int b) { try { int c = a / b; } catch (Exception e) { System.out.print("Exception "); } finally { System.out.println("Finally"); } 1) Prints out: Exception Finally 2) Prints out: Finally 3) Prints out: Exception 4) No output Answer : 1 Which of the following is a legal return type of a method overloading the following method:
public void add(int a) {...} 1) void 2) int 3) Can be anything Answer : 3 Which of the following statements is correct for a method which is overriding the following method: public void add(int a) {...} 1) the overriding method must return void 2) the overriding method must return int 3) the overriding method can return whatever it likes Answer : 1 Given the following classes defined in separate files, what will be the effect of compiling and running this class Test? class Vehicle { public void drive() { System.out.println("Vehicle: drive"); } } class Car extends Vehicle { public void drive() { System.out.println("Car: drive"); } } public class Test { public static void main (String args []) { Vehicle v;
Car c; v = new Vehicle(); c = new Car(); v.drive(); c.drive(); v = c; v.drive(); } } 1) Generates a Compiler error on the statement v= c; 2) Generates runtime error on the statement v= c; 3) Prints out: Vehicle: drive Car: drive Car: drive 4) Prints out: Vehicle: drive Car: drive Vehicle: drive Answer : 3 Where in a constructor, can you place a call to a constructor defined in the super class? 1) Anywhere 2) The first statement in the constructor 3) The last statement in the constructor 4) You can't call super in a constructor
Answer : 2 Which variables can an inner class access from the class which encapsulates it? (multiple) 1) All static variables 2) All final variables 3) All instance variables 4) Only final instance variables 5) Only final static variables Answer : 1,2,3 What class must an inner class extend: 1) The top level class 2) The Object class 3) Any class or interface 4) It must extend an interface Answer 3 In the following code, which is the earliest statement, where the object originally held in e, may be garbage collected: 1. public class Test { 2. public static void main (String args []) { 3. Employee e = new Employee("Bob", 48); 4. e.calculatePay(); 5. System.out.println(e.printDetails()); 6. e = null; 7. e = new Employee("Denise", 36); 8. e.calculatePay(); 9. System.out.println(e.printDetails());
10. } 11. } 1) Line 10 2) Line 11 3) Line 7 4) Line 8 5) Never Answer : 3 What is the name of the interface that can be used to define a class that can execute within its own thread? 1) Runnable 2) Run 3) Threadable 4) Thread 5) Executable Answer : 1 What is the name of the method used to schedule a thread for execution? 1) init(); 2) start(); 3) run(); 4) resume(); 5) sleep(); Answer : 2 Which methods may cause a thread to stop executing? (multiple) 1) sleep();
2) stop(); 3) yield(); 4) wait(); 5) notify(); 6) notifyAll() 7) synchronized() Answer : 1,2,3,4 Which of the following would create a text field able to display 10 characters (assuming a fixed size font) displaying the initial string "hello": 1) new TextField("hello", 10); 2) new TextField("hello"); 3) new textField(10); 4) new TextField(); Answer : 1 Which of the following methods are defined on the Graphics class: (multiple) 1) drawLine(int, int, int, int) 2) drawImage(Image, int, int, ImageObserver) 3) drawString(String, int, int) 4) add(Component); 5) setVisible(boolean); 6) setLayout(Object); Answer : 1,2,3 Which of the following layout managers honours the preferred size of a component: (multiple) 1) CardLayout
2) FlowLayout 3) BorderLayout 4) GridLayout Answer : 2 Given the following code what is the effect of a being 5: public class Test { public void add(int a) { loop: for (int i = 1; i < 3; i++){ for (int j = 1; j < 3; j++) { if (a == 5) { break loop; } System.out.println(i * j); } } } } 1) Generate a runtime error 2) Throw an ArrayIndexOutOfBoundsException 3) Print the values: 1, 2, 2, 4 4) Produces no output Answer : 4 What is the effect of issuing a wait() method on an object 1) If a notify() method has already been sent to that object then it has no effect 2) The object issuing the call to wait() will halt until another object sends a notify() or notifyAll() method
3) An exception will be raised 4) The object issuing the call to wait() will be automatically synchronized with any other objects using the receiving object. Answer : 2 The layout of a container can be altered using which of the following methods: (multiple) 1) setLayout(aLayoutManager); 2) addLayout(aLayoutManager); 3) layout(aLayoutManager); 4) setLayoutManager(aLayoutManager); Answer : 1 Using a FlowLayout manager, which is the correct way to add elements to a container: 1) add(component); 2) add("Center", component); 3) add(x, y, component); 4) set(component); Answer : 1 Given that a Button can generate an ActionEvent which listener would you expect to have to implement, in a class which would handle this event? 1) FocusListener 2) ComponentListener 3) WindowListener 4) ActionListener 5) ItemListener Answer : 4 Which of the following, are valid return types, for listener methods: 1) boolean
2) the type of event handled 3) void 4) Component Answer : 3 Assuming we have a class which implements the ActionListener interface, which method should be used to register this with a Button? 1) addListener(*); 2) addActionListener(*); 3) addButtonListener(*); 4) setListener(*); Answer : 2 In order to cause the paint(Graphics) method to execute, which of the following is the most appropriate method to call: 1) paint() 2) repaint() 3) paint(Graphics) 4) update(Graphics) 5) None - you should never cause paint(Graphics) to execute Answer : 2 Which of the following illustrates the correct way to pass a parameter into an applet: 1) 2) 3) 4) Answer : 2 Which of the following correctly illustrate how an InputStreamReader can be created: (multiple)
1) new InputStreamReader(new FileInputStream("data")); 2) new InputStreamReader(new FileReader("data")); 3) new InputStreamReader(new BufferedReader("data")); 4) new InputStreamReader("data"); 5) new InputStreamReader(System.in); Answer : 1,5 What is the permanent effect on the file system of writing data to a new FileWriter("report"), given the file report already exists? 1) The data is appended to the file 2) The file is replaced with a new file 3) An exception is raised as the file already exists 4) The data is written to random locations within the file Answer : 2 What is the effect of adding the sixth element to a vector created in the following manner: new Vector(5, 10); 1) An IndexOutOfBounds exception is raised. 2) The vector grows in size to a capacity of 10 elements 3) The vector grows in size to a capacity of 15 elements 4) Nothing, the vector will have grown when the fifth element was added Answer : 3 What is the result of executing the following code when the value of x is 2: switch (x) { case 1: System.out.println(1); case 2: case 3:
System.out.println(3); case 4: System.out.println(4); } 1) Nothing is printed out 2) The value 3 is printed out 3) The values 3 and 4 are printed out 4) The values 1, 3 and 4 are printed out Answer : 3 What is the result of compiling and running the Second class? Consider the following example: class First { public First (String s) { System.out.println(s); } } public class Second extends First { public static void main(String args []) { new Second(); } } 1) Nothing happens 2) A string is printed to the standard out 3) An instance of the class First is generated 4) An instance of the class Second is created
5) An exception is raised at runtime stating that there is no null parameter constructor in class First. 6) The class second will not compile as there is no null parameter constructor in the class First Answer : 6 What is the result of executing the following fragment of code: boolean flag = false; if (flag = true) { System.out.println("true"); } else { System.out.println("false"); } 1) true is printed to standard out 2) false is printed to standard out 3) An exception is raised 4) Nothing happens Answer : 1 Consider the following classes. What is the result of compiling and running this class? public class Test { public static void test() { this.print(); } public static void print() { System.out.println("Test"); } public static void main(String args []) { test();
} } (multiple) 1) The string Test is printed to the standard out. 2) A runtime exception is raised stating that an object has not been created. 3) Nothing is printed to the standard output. 4) An exception is raised stating that the method test cannot be found. 5) An exception is raised stating that the variable this can only be used within an instance. 6) The class fails to compile stating that the variable this is undefined. Answer : 6 Examine the following class definition: public class Test { public static void test() { print(); } public static void print() { System.out.println("Test"); } public void print() { System.out.println("Another Test"); } } What is the result of compiling this class: 1) A successful compilation. 2) A warning stating that the class has no main method.
3) An error stating that there is a duplicated method. 4) An error stating that the method test() will call one or other of the print() methods. Answer : 3 What is the result of compiling and executing the following Java class: public class ThreadTest extends Thread { public void run() { System.out.println("In run"); suspend(); resume(); System.out.println("Leaving run"); } public static void main(String args []) { (new ThreadTest()).start(); } } 1) Compilation will fail in the method main. 2) Compilation will fail in the method run. 3) A warning will be generated for method run. 4) The string "In run" will be printed to standard out. 5) Both strings will be printed to standard out. 6) Nothing will happen. Answer : 4 Given the following sequence of Java statements, Which of the following options are true: 1. StringBuffer sb = new StringBuffer("abc"); 2. String s = new String("abc");
3. sb.append("def"); 4. s.append("def"); 5. sb.insert(1, "zzz"); 6. s.concat(sb); 7. s.trim(); (multiple) 1) The compiler would generate an error for line 1. 2) The compiler would generate an error for line 2. 3) The compiler would generate an error for line 3. 4) The compiler would generate an error for line 4. 5) The compiler would generate an error for line 5. 6) The compiler would generate an error for line 6. 7) The compiler would generate an error for line 7. Answer : 4,6 What is the result of executing the following Java class: import java.awt.*; public class FrameTest extends Frame { public FrameTest() { add (new Button("First")); add (new Button("Second")); add (new Button("Third")); pack(); setVisible(true); } public static void main(String args []) { new FrameTest();
} } 1) Nothing happens. 2) Three buttons are displayed across a window. 3) A runtime exception is generated (no layout manager specified). 4) Only the "first" button is displayed. 5) Only the "second" button is displayed. 6) Only the "third" button is displayed. Answer : 6 Consider the following tags and attributes of tags, which can be used with the and tags? 1. CODEBASE 2. ALT 3. NAME 4. CLASS 5. JAVAC 6. HORIZONTALSPACE 7. VERTICALSPACE 8. WIDTH 9. PARAM 10. JAR (multiple) 1) line 1, 2, 3 2) line 2, 5, 6, 7 3) line 3, 4, 5 4) line 8, 9, 10
5) line 8, 9 Answer : 1,5 Which of the following is a legal way to construct a RandomAccessFile: 1) RandomAccessFile("data", "r"); 2) RandomAccessFile("r", "data"); 3) RandomAccessFile("data", "read"); 4) RandomAccessFile("read", "data"); Answer : 1 Carefully examine the following code, When will the string "Hi there" be pr inted? public class StaticTest { static { System.out.println("Hi there"); } public void print() { System.out.println("Hello"); } public static void main(String args []) { StaticTest st1 = new StaticTest(); st1.print(); StaticTest st2 = new StaticTest(); st2.print(); } } 1) Never. 2) Each time a new instance is created. 3) Once when the class is first loaded into the Java virtual machine.
4) Only when the static method is called explicitly. Answer : 3 What is the result of the following program: public class Test { public static void main (String args []) { boolean a = false; if (a = true) System.out.println("Hello"); else System.out.println("Goodbye"); } } 1) Program produces no output but terminates correctly. 2) Program does not terminate. 3) Prints out "Hello" 4) Prints out "Goodbye" Answer : 3 Examine the following code, it includes an inner class, what is the result: public final class Test4 { class Inner { void test() { if (Test4.this.flag); { sample(); } } }
private boolean flag = true; public void sample() { System.out.println("Sample"); } public Test4() { (new Inner()).test(); } public static void main(String args []) { new Test4(); } } 1) Prints out "Sample" 2) Program produces no output but terminates correctly. 3) Program does not terminate. 4) The program will not compile Answer : 1 Carefully examine the following class: public class Test5 { public static void main (String args []) { /* This is the start of a comment if (true) { Test5 = new test5(); System.out.println("Done the test"); } /* This is another comment */ System.out.println ("The end");
} } 1) Prints out "Done the test" and nothing else. 2) Program produces no output but terminates correctly. 3) Program does not terminate. 4) The program will not compile. 5) The program generates a runtime exception. 6) The program prints out "The end" and nothing else. 7) The program prints out "Done the test" and "The end" Answer : 6 What is the result of compiling and running the following applet: import java.applet.Applet; import java.awt.*; public class Sample extends Applet { private String text = "Hello World"; public void init() { add(new Label(text)); } public Sample (String string) { text = string; } } It is accessed form the following HTML page: Sample Applet
1) Prints "Hello World". 2) Generates a runtime error. 3) Does nothing. 4) Generates a compile time error. Answer : 2 What is the effect of compiling and (if possible) running this class: public class Calc { public static void main (String args []) { int total = 0; for (int i = 0, j = 10; total > 30; ++i, --j) { System.out.println(" i = " + i + " : j = " + j); total += (i + j); } System.out.println("Total " + total); } } 1) Produce a runtime error 2) Produce a compile time error 3) Print out "Total 0" 4) Generate the following as output: i = 0 : j = 10 i= 1: j=9 i= 2: j=8
Total 30 Answer : 3
Utility Package 1) What is the Vector class? ANSWER : The Vector class provides the capability to implement a growable array of objects. 2) What is the Set interface? ANSWER : The Set interface provides methods for accessing the elements of a finite mathematical set.Sets do not allow duplicate elements. 3) What is Dictionary class? ANSWER : The Dictionary class is the abstarct super class of Hashtable and Properties class.Dictionary provides the abstarct functions used to store and retrieve objects by key-value.This class allows any object to be used as a key or value. 4) What is the Hashtable class? ANSWER : The Hashtable class implements a hash table data structure. A hash table indexes and stores objects in a dictionary using hash codes as the objects' keys. Hash codes are integer values that identify objects. 5) What is the Properties class? Answer : The properties class is a subclass of Hashtable that can be read from or written to a stream.It also provides the capability to specify a set of default values to be used if a specified key is not found in the table. We have two methods load() and save(). 6) What changes are needed to make the following prg to compile? import java.util.*; class Ques{ public static void main (String args[]) { String s1 = "abc"; String s2 = "def"; Vector v = new Vector();
v.add(s1); v.add(s2); String s3 = v.elementAt(0) + v.elementAt(1); System.out.println(s3); } } ANSWER : Declare Ques as public B) Cast v.elementAt(0) to a String C) Cast v.elementAt(1) to an Object. D) Import java.lang ANSWER : B) Cast v.elementAt(0) to a String
8) What is the output of the prg. import java.util.*; class Ques{ public static void main (String args[]) { String s1 = "abc"; String s2 = "def"; Stack stack = new Stack(); stack.push(s1); stack.push(s2); try{ String s3 = (String) stack.pop() + (String) stack.pop() ; System.out.println(s3); }catch (EmptyStackException ex){} } } ANSWER : abcdef B) defabc C) abcabc D) defdef
ANSWER : B) defabc 9) Which of the following may have duplicate elements? ANSWER : Collection B) List C) Map D) Set ANSWER : A and B Neither a Map nor a Set may have duplicate elements. 10) Can null value be added to a List? ANSWER : Yes.A Null value may be added to any List. 11) What is the output of the following prg. import java.util.*; class Ques{ public static void main (String args[]) { HashSet set = new HashSet(); String s1 = "abc"; String s2 = "def"; String s3 = ""; set.add(s1); set.add(s2); set.add(s1); set.add(s2); Iterator i = set.iterator(); while(i.hasNext()){ s3 += (String) i.next(); } System.out.println(s3); } } A) abcdefabcdef B) defabcdefabc C) fedcbafedcba D) defabc
ANSWER : D) defabc. Sets may not have duplicate elements. 12) Which of the following java.util classes support internationalization? A) Locale B) ResourceBundle C) Country D) Language ANSWER : A and B . Country and Language are not java.util classes. 13) What is the ResourceBundle? The ResourceBundle class also supports internationalization. ResourceBundle subclasses are used to store locale-specific resources that can be loaded by a program to tailor the program's appearence to the paticular locale in which it is being run. Resource Bundles provide the capability to isolate a program's locale-specific resources in a standard and modular manner. 14) How are Observer Interface and Observable class, in java.util package, used? ANSWER : Objects that subclass the Observable class maintain a list of Observers. When an Observable object is updated it invokes the update() method of each of its observers to notify the observers that it has changed state. The Observer interface is implemented by objects that observe Observable objects. 15) Which java.util classes and interfaces support event handling? ANSWER : The EventObject class and the EventListener interface support event processing. 16) Does java provide standard iterator functions for inspecting a collection of objects? ANSWER : The Enumeration interface in the java.util package provides a framework for stepping once through a collection of objects. We have two methods in that interface. public interface Enumeration { boolean hasMoreElements(); Object nextElement(); } 17) The Math.random method is too limited for my needs- How can I generate random numbers more flexibly? ANSWER : The random method in Math class provide quick, convienient access to random numbers, but more power and flexibility use the Random class in the java.util package.
double doubleval = Math.random(); The Random class provide methods returning float, int, double, and long values. nextFloat() // type float; 0.0
